scholarly journals Memoirs: On the Blood-Vascular System of the Earthworm Pheretima, and the Course of the Circulation in Earthworms

1921 ◽  
Vol s2-65 (259) ◽  
pp. 349-393
Author(s):  
KARM NARAYAN BAHL
Keyword(s):  
Body Wall ◽  
Vascular System ◽  
Blood System ◽  
The Body ◽  
Dorsal Vessel ◽  
The Third ◽  
Arterial Trunk ◽  
Venous Function ◽  
Circulation Of The Blood ◽  
Close Parallelism

1. The typical arrangement of the blood-system in Pheretima occurs in the region of the body behind the fourteenth segment, the first fourteen segments forming the cephalized region. The main longitudinal trunks are the same as in Lumbricus, except that the lateral neurals are absent as in Allolobophora. The dorsal vessel receives two pairs of dorso-intestinals and one pair of commissurals in each segment behind the cephalized region. 2. The intestinal blood-plexus is both an external and an internal one, and three regions can easily be distinguished. The first is internal, and extends from the fourteenth to the twenty-sixth segment; the second is both external and internal, is co existent with the typhlosole, and extends over the larger part of the gut; and the third is only external, and is confined to the rectal or post-typhlosolar part of the gut (last twenty-three to twenty-six segments) 3. The commissural vessel of Pheretima is a compound vessel, and represents both the ‘dorso-sous-nervien’ of Lumbricus and the intestino-tegumentary of Megascolex. The capillaries of the integument are not like those of Lumbricus but like those of Moniligaster, and there is a close ‘parallelism’ between an ‘artery’ and a ‘vein’ in the body-wall, in which the two pass into each other through a number of capillary loops. 4. There are four pairs of ‘hearts’ which connect the dorsal with the ventral vessel, and five pairs which supply blood directly to the various organs in the cephalized region. There are two pairs of non-contractile ‘anterior loops’ connecting the lateral oesophageals with the supra-intestinals, these loops being the counterpart of the connexions of the lateral oesophageals with the dorsal and the parietal in the tenth and twelfth segments respectively of Lumbricus. The subneural Tessel is absent in the first fourteen segments, and is continuous with the lateral oesophageals of the anterior region. 5. As regards the course of circulation of the blood, the chief fact is that the dorsal vessel is wholly ‘venous’ behind the ‘hearts’ and wholly ‘arterial’ in the region of the ‘hearts’ and in front (the whole of the cephalized region). The examination of valves and experiments by cutting and pinching the blood-vessels in Pheretima confirm the results of Johnstone for Lumbricus as regards the course of blood in dorsointestinals and commissurals and make Bourne's theory untenable. The ventral vessel is the arterial trunk throughout, while the venous function of the dorsal and subneural behind is taken up by the lateral oesophageals in the cephalized region. The thin-walled and non-contractile ‘loops’ of the tenth and eleventh segments must be distinguished from the thick walled and contractile ‘hearts’ of the other cephalized segments, the ‘loops’ being the channels for conveying blood from the lateral oesophageals to the supra-intestinals.

scholarly journals The Blood-system in the Serpulimorpha (Annelida, Polychaeta)

1950 ◽  
Vol s3-91 (16) ◽  
pp. 369-378
Author(s):  
JEAN HANSON
Keyword(s):  
Blood Supply ◽  
Peripheral Blood ◽  
Body Wall ◽  
Blood System ◽  
The Body ◽  
Dorsal Vessel ◽  
The Family ◽  
Body Wall Musculature

1. The blood-system in sabellids of the following genera is described: Sabella, Potamilla, Branchiomma, Dasychone, Amphiglena, Fabricia, Jasmineira, Dialychone, and Myxicola. 2. The central blood-system of Sabella is typical of the family, but the peripheral blood-system is variable. 3. The dorsal vessel lacks the valve and muscular sphincter found in some serpulids. 4. Lateral vessels are present only in Sabella and Dasychone. 5. The differences and similarities between sabellid and serpulid blood-systems are discussed. Special attention is given to the functions of sub-epidermal and coelomic capillaries and the blood-supply of the body-wall musculature.

Memoirs: The Vascular System of Octoehaetus thomasi

1935 ◽  
Vol s2-78 (310) ◽  
pp. 251-270
Author(s):  
MAURICE BLEAKLY
Keyword(s):  
Vascular System ◽  
The Body ◽  
Anterior Region ◽  
Common Trunk ◽  
Dorsal Vessel ◽  
Small Vessels ◽  
Arterial Trunk ◽  
Pass Through

1. Posteriorly to the gizzard the dorsal vessel of O. thomasi is double, consisting of two tubes joined by a short connecting vessel anterior to the septum in each segment. 2. There are six pairs of strongly contractile hearts in segments 8-13. The latero-intestinal hearts in segments 10-13 receive blood from the dorsal vessel and from a common trunk from the supra-intestinal and latero-oesophageal vessels, and supply blood to the ventral vessel. The lateral hearts receive blood from the dorsal vessel and supply ventro-tegumentary and ventral vessels. For complete circulation all blood must pass through the hearts. 3. The ventral vessel, which is not contractile, receives blood from the hearts; posteriorly to the hearts the flow is backward in the ventral vessel and outward via ventro-tegumentaries and ventro-intestinals to the body and gut; anteriorly to the hearts the flow is forward, the blood leaving the ventral vessel by the commissures from which the ventro-tegumentaries of the anterior region arise. The ventral vessel is the main arterial trunk. 4. Posteriorly to the hearts the dorsal vessel collects blood from the body and gut by dorso-tegumentaries and dorso-intestinals. The flow in the dorsal vessel, which is contractile, is forward. Blood leaves the dorsal vessel through small vessels to the laterointestinal hearts, and larger vessels to the lateral hearts. Anteriorly to the hearts, the commissures and all vessels connected with the dorsal vessel receive blood from it. Thus, posteriorly to the hearts the dorsal vessel is venous, and anteriorly to the hearts arterial, in character. 5. Blood from the anterior region is returned by paired latero-oesophageal vessels to the supra-intestinal vessel and to the latero-intestinal hearts. The latero-oesophageal vessels and the supra-intestinal vessels are the main venous trunks in the anterior region. 6. There is no sub-neural vessel.

The Blood Vascular System of Nephtys (Annelida, Polychaeta)

1956 ◽  
Vol s3-97 (38) ◽  
pp. 235-249
Author(s):  
R. B. CLARK
Keyword(s):  
Body Wall ◽  
Vascular System ◽  
Close Association ◽  
Circulatory System ◽  
Ventral Surface ◽  
Blood Stream ◽  
Neurosecretory Cells ◽  
The Body ◽  
Dorsal Vessel ◽  
The Brain

The four longitudinal vessels of the circulatory system of Nephtys californiensis are dorsal, sub-intestinal, and neural, the latter being paired. There is a complete longitudinal circulation; the dorsal vessel communicates with the sub-intestinal by way of the proboscidial circulation and with the neural by way of the circum-oral vessels. In each middle and posterior segment segmental vessels from each of the longitudinal trunks carry blood to and from the parapodia and body-wall. The segmental circulation is completed by a circum-intestinal vessel connecting the dorsal and subintestinal vessels in each segment and an intersegmental branch connecting the dorsal and sub-intestinal segmental vessels. A trans-septal branch of the neural segmental vessel communicates with the sub-intestinal segmental vessel. This arrangement is modified in anterior segments which house the muscular, eversible pharynx, and no blood-vessels cross the coelom except by running through the body-wall. On anatomical grounds and by comparison with other polychaetes it seems likely that segmental is subordinate to longitudinal circulation. There are no endothelial capillaries such as have been described in some other polychaetes; instead there are numerous blindending vessels the walls of which are composed of the same three layers as other vessels and which are probably contractile. The dorsal vessel, where it is in contact with the ventral surface of the supra-oesophageal ganglion, forms a plexus in close association with a modified part of the brain capsule and a special axonal tract within the ganglion. It is thought that by way of this ‘cerebro-vascular complex’, hormones produced in the neurosecretory cells of the brain pass into the blood-stream.

Memoirs: On the Communication between the Cœlom and the Vascular System in the Leech, Hirudo medicinalis

1899 ◽  
Vol s2-42 (168) ◽  
pp. 477-495
Author(s):  
EDWIN S. GOODRICH
Keyword(s):  
Body Wall ◽  
Vascular System ◽  
The Body ◽  
The Other ◽  
True Nature ◽  
Annular Channels ◽  
Abdominal Vessels ◽  
Two Systems ◽  
Imperfect Knowledge ◽  
The One

According to the foregoing account, the evidence of carefully executed injections strongly favours the view that a continuity exists between the contractile vascular system and the noncontractile sinus system in Hirudo. This continuity is proved to exist in various regions of the body by means of serial sections. The communication takes place through the capillary systems. The hæmolymph system of Hirudo consists of four main longitudinal trunks, sending out transverse branches to the body-wall. The dorsal branches of the lateral vessels pass into small annular vessels communicating with the plexus of minute capillaries in the epidermis. From these, again, arise capillaries going to small sinuses which run into the lateral transverse sinuses, and so into the dorsal sinus. Similarly (he ventral sinus sends annular sinuses along the ventral region of the body-wall opening into the epidermal plexus, whence arise capillaries joining the latero-abdominal vessels. Continuity between the two systems has also been shown to take place by means of capillaries on the wall of the alimentary canal, and probably exists on the other internal organs of the body. Two questions still remain to be solved: firstly, as to the circulation of the hæmolymph; secondly, as to the exact homology of the channels in which it flows. With respect to the first of these problems, I have no direct observations to record; but it may be pointed out that the presence of the valves described above show, at least, that the hæmolymph must flow in a constant direction--that there is a real circulation, not a mere motion backwards and forwards. It seems to me extremely probable that the annular vessels collect the oxygenated blood from the epidermal plexus, and carry it into the latero-dorsal and latero-lateral vessels, whence it would be pumped into the lateral vessels. From these some of the hæmolymph must be carried by the latero-abdominal vessels to the various organs of the body, and to the ventral cutaneous plexus. The annular sinuses would collect it from this plexus and carry it into the ventral sinus. The abdominodorsals and the dorsal sinus would appear to supply the dorsal and lateral cutaneous plexus. We are left in considerable uncertainty as to the true nature of some of the spaces. That the lateral vessels belong to the real vascular system, and that the ventral sinus and perinephrostomial sinuses belong to the true cœlomic system, seems to be clearly established both by comparative anatomy and by the embryological researches of Bürger (2). This observer, however, could not trace the dorsal sinus to a cœlomic origin, and since its branches bear the same relation to the cutaneous plexus as those of the latero-abdominal vessels, I am inclined to think that the dorsal sinus may represent the dorsal vessel of other annelids. In that case the cœlomic cavities do not persist dorsally, or have never reached the median dorsal region in the Gnathobdellidæ. The annular channels may possibly represent the annular cœlomic lacunæ so well described and figured by Oka in Clepsine (10), and it may perhaps be through them that the chief communication between the cœlom and the vascular system has been established. The observation of the some-what variable relations of these annular channels tends to support this view. With the very imperfect knowledge of the development of the cœlom and blood-vessels in Hirudo at our disposal, we cannot say for certain at present where the one ends and the other begins, nor whether a given capillary really belongs to the one or the other. Nor can we safely conjecture how the continuity has actually taken place. But one thing seems fairly certain, namely, that it is not only by means of the botryoidal channels that the communication has been brought about. It is very tempting to compare the leech with the Vertebrate, in which a third system of spaces--the lymphatic system--has been interpolated, allowing a communication to take place between the originally distinct cœlom and blood-vascular system.1 But the botryoidal tissue is not so inter-polated in the case of Hirudo; if it were obliterated, the two systems would still be in free continuity by means of capillaries. The botryoidal channels would seem to be rather of the nature of a by-path, through which the hæmolymph does not necessarily circulate. In this connection it should be mentioned that in sections they are rarely seen to be as much distended with the fluid as the neighbouring capillaries of similar size. Whatever may be the process whereby the continuity between the cœlom and vascular system has been established in the Gnathobdellidæ, there can be little doubt that it is a secondary condition, and that the structure of such a form as Acanthobdella, in which a closed blood-system lies in a normally developed cœlom, is really the more primitive.

The Blood-system in the Serpulimorpha (Annelida, Polychaeta)

1950 ◽  
Vol s3-91 (14) ◽  
pp. 111-129
Author(s):  
JEAN HANSON
Keyword(s):  
Body Wall ◽  
Ventral Surface ◽  
Blood System ◽  
The Body ◽  
Sphincter Muscle ◽  
Central System ◽  
Respiratory Organ ◽  
Blind Ending ◽  
Usual Manner ◽  
Vascular Plexuses

1. An account will be given of the anatomy of the blood-system of Pomatoceros triqueter, and of comparative observations on the following serpulids: Serpula vermicularis, S. lo-biancoi, Hydroides norvegica, Vermiliopsis infundibulum, Salmacina incrustans, Protula intestinum, P. tubularia, Apomatus ampulliferus, A. similis, Spirorbis militaris, and S. corrugatus. 2. In all species there is a central blood-system of large vessels in which blood circulates in the usual manner, and a peripheral system of small blind-ending vessels which are alternately full and empty, receiving their blood from the central system, then returning it along the same channels to the central system. 3. The central blood-system is as follows: Blood moves from the tip of the abdomen to the front of the thorax through a sinus enveloping the alimentary canal. Anteriorly it passes through dorsal, transverse, and circum-oesophageal vessels to a ventral vessel in which it moves backwards to the tip of the abdomen. A pair of ring vessels connects the ventral vessel with the sinus at the posterior end of each segment. 4. The anterior end of the dorsal vessel in Pomatoceros triqueter, Serpula vermicularis, Hydroides norvegica, and Vermiliopsis infundibulum is surrounded by a sphincter muscle of unknown function, and contains a muscular valve which probably obstructs the back-flow of blood from the transverse vessel. Protula intestinum possesses the valve but lacks the sphincter. Salmacina incrustans and Spirorbis militaris have neither valve nor sphincter. 5. The peripheral blood-system has the following components: the branchial vessels with branches in the crown; the vessels of the collar and lips; the peri-oesophageal plexuses; the trans-septal vessels supplying the body-wall, parapodia, and thoracic membrane. 6. In Pomatoceros triqueter the opercular vessel is spirally coiled, but in other serpulids it is characteristically branched. 7. When Pomatoceros withdraws into its tube, movement of blood in the crown ceases. The operculum is therefore not used as a special respiratory organ when the crown is retracted. 8. The oesophagus of Pomatoceros is surrounded by two independent blind-ending vascular plexuses, an outer plexus communicating with the gut sinus and an inner plexus with the circum-oesophageal vessels. Serpula vermicularis is probably the same. Hydroides norvegica and Protula intestinum lack the outer plexus. Salmacina and Spirorbis have neither plexus. 9. The body-wall of each segment derives its blood-supply from trans-septal branches of the ring vessels of the preceding segment. In Salmacina and Spirorbis these trans-septal vessels are unbranched. In larger serpulids they have numerous branches under the epidermis, in the parapodia, and in some cases on the coelomic surface of the body-wall. Branches of the thoracic trans-septal vessels supply the thoracic membrane. In all species except Salmacina, Spirorbis, and Protula intestinum he thoracic trans-septal vessels end ventrally in two superficial ventro-lateral longitudinal vessels which communicate either with the circum-oesophageal vessels or with the ventral vessel. In P. intestinum the thoracic trans-septal vessels enter the ventral vessel directly. The pattern of superficial vessels on the ventral surface of the thorax is useful for identifying specimens. 10. Lateral vessels, such as are found in Sabella, are absent in all serpulids.

scholarly journals The unc-45 gene of Caenorhabditis elegans is an essential muscle-affecting gene with maternal expression.

Genetics ◽  
1990 ◽  
Vol 126 (2) ◽  
pp. 345-353
Author(s):  
L Venolia ◽  
R H Waterston
Keyword(s):  
Gene Product ◽  
Body Wall ◽  
The Body ◽  
Temperature Sensitive ◽  
Myosin Heavy Chain Isoform ◽  
Heavy Chains ◽  
C Elegans ◽  
The Third ◽  
Pharyngeal Muscles ◽  
Novel Alleles

Abstract We have isolated three novel alleles of the unc-45 locus in C. elegans, that are recessive lethals. Two of these alleles, when homozygous, result in a nearly total loss of muscle contraction with a concomitant arrest of development and a displacement of muscle cells. The third allele is similar, but showed maternal rescue by a wild-type allele. All previously identified unc-45 alleles were temperature sensitive and, although they produced paralysis of adult animals, all were homozygous viable. Prior genetic studies with these temperature sensitive alleles had suggested that at least one function of the unc-45 gene product was to interact with the major myosin heavy chain isoform, MHC B, of body wall muscles. Our observations of the lethal alleles suggest that the unc-45 product normally interacts with additional muscle components in both the body wall and pharyngeal muscles. In particular, we suggest that the unc-45 product might interact with all four myosin heavy chains: MHC B; MHC A; and the pharyngeal isoforms, MHC C and MHC D. Maternal rescue of the lethality of the third allele shows that the unc-45 gene product is present in the oocytes, although it may not be necessary until late in development when myofilaments begin to assemble.

Skeletal homologies of echinoderms

1997 ◽  
Vol 3 ◽  
pp. 305-335 ◽  
Author(s):  
Rich Mooi ◽  
Bruno David
Keyword(s):  
Recent Work ◽  
Early Development ◽  
Body Wall ◽  
Vascular System ◽  
Axial Skeleton ◽  
Morphological Characters ◽  
The Body ◽  
Larval Body

The impressive array of disparity within the Echinodermata can be explained by the interplay of components (particularly skeletal elements) making up two major body wall regions: axial and extraxial. Axial skeleton comprises paired plate columns of the ambulacra, formed according to the Ocular Plate Rule (OPR) and in association with the water vascular system. Extraxial skeleton (subdivided into two subtypes: perforate and imperforate) is not formed according to the OPR, and new elements can be added anywhere and at any time within extraxial body wall. Recent work on early development of echinoderms reveals that axial skeleton is formed as an integral part of the rudiment, but that extraxial skeleton is derived from the non-rudiment part of the larval body. In addition to displaying such fundamental embryological and ontogenetic differences, the body wall regions have distinctive distributions and topologies that can be used to formulate criteria for their identification in any echinoderm regardless of how esoteric their morphology might be. Like the system of homologies that has long been established for vertebrates, the model of axial and extraxial skeletal types can be used to explore relationships among Recent and fossil taxa alike. Application of the model also leads to reassessment of previously published morphological characters and phylogenies.

Electron-microscopical observations on the body wall of the third-stage larva of Haemonchus placei

Parasitology ◽  
1970 ◽  
Vol 60 (3) ◽  
pp. 411-416 ◽  
Author(s):  
Kenneth Smith
Keyword(s):  
Body Wall ◽  
Muscle Cells ◽  
Cortical Layer ◽  
The Body ◽  
Stage Larva ◽  
Dense Layer ◽  
The Third ◽  
Third Stage ◽  
Electron Microscopical ◽  
Inner Cortex

SUMMARYThe ultrastructure of the body wall of the third-stage larva of Haemonckus placei was studied. The cuticle was found to consist of eight layers: a thin outer layer, a membrane-bounded layer, an electron-dense layer, a thin irregular layer, an inner cortical layer, a matrix layer, a striated layer and a fibril layer. Interposed between the inner cortex and matrix were two transverse fibres.The region between the fibril layers and the contractile part of the muscle cells was occupied by the hypodermis, which enlarged to form the dorsal, ventral and lateral cords. Within the cords lay hypodermal cells, nerves, crystalline inclusions and an excretory canal.The sarcoplasmic part of the muscle cells was rich in glycogen and contained numerous mitochondria. Myofibrils of two types were present in the contractile part of the cell.I am grateful to Dr D. W. Brocklesby for his help and advice and to Mr E. Harness for the production and supply of third-stage larvae. I would also like to thank Dr D. L. Lee and Mr W. G. MacMillan for helpful discussions.

scholarly journals Memoirs: On the Development of the ‘Enteronephric’ type of Nephridial system found in Indian Earthworms of the genus Pheretima’

1922 ◽  
Vol s2-66 (261) ◽  
pp. 49-103
Author(s):  
KARM NARAYAN BAHL
Keyword(s):  
Body Wall ◽  
Lateral Position ◽  
The Body ◽  
Common Origin ◽  
Advanced Stage ◽  
Dorsal Vessel ◽  
Stages Of Development ◽  
Stage Of Development ◽  
Straight Line ◽  
Excretory Canals

1. The three kinds of nephridia--integumentary, septal, and pharyngeal--appear at successive stages of development of the embryo; the integumentary preceding the septal and pharyngeal, both of which develop simultaneously. 2. All the three kinds can be traced back to the original row of nephridial cells of ectodermal origin. Thus all the different nephridia are ultimately derived from one common origin. 3. The primary pair of integumentary nephridia are the first to appear from a ‘retro-peritoneal’ group of cells. The rudiments lack the ‘funnel-cell’, and consequently a ‘coolomic’ funnel is never developed in these nephridia. They open to the exterior on the body-wall. 4. These primary integumentary nephridia do not appear in the same position in successive segments of the embryo, but are irregularly distributed all over the body-wall. 5. The septal primary nephridia can be traced back to a group of nephridial cells, including the ‘funnel-cell’, which make their way into each septum between its two adjoining peritoneal lamellae. 6. The primary septal nephridia have always a well-developed pre-septal funnel, and appear along a straight line on both sides of the dorsal vessel. They appear after the primary integumentary pair has reached a fairly advanced stage of development. 7. The secondary nephridia of both the integumentary and septal types are not budded off from the primary nephridia, but the rudiments of all have a common origin and separate early. They resemble the primaries in every respect, except that in the case of the septal secondaries the funnel is either pre-septal or post-septal. 8. The terminal ducts of the primary septal nephridia form the dorsal portions of the septal excretory canals on the septa, and the canals of both sides form the supra-intestinal duct on meeting the mid-dorsal line above the gut. The segmontal ductules establishing a communication between the supraintestinal duct and the lumen of the gut appear soon after the formation of the supra-intestinal ducts. 9. The primary pharyngeal nephridia of the fourth, fifth, and sixth segments develop from a ‘retro-peritoneal’ group of cells like the integumentary ones, and have long ducts reaching the wall of the pharynx. Secondary nephridia are formed as successive buds on the ducts, anterior to the primary nephridia. 10. The possible phylogenetic stages in the evolution of the ‘enteronephric’ type of nephridia are as follows : (1) the severance of the connexion between the septal funnel and the body of the nephridium; (2) migration of the severed portion, i. e. the ‘funnel-cell’, together with some other nephridial cells from a ventral to a lateral position in the embryo ; (3) the growth of this severed portion into a septal nephridium and the acquisition by the latter of an opening into the gut; (4) the elongation of the terminal ducts of all septal nephridia towards the mid-dorsal line (induced by the course of commissural vessels) and the formation of continuous supra-intestinal ducts. It is problematic whether the severance of the connexion between the funnel and the body of the nephridium took place before or after the connexion of the nephridium with the gut.

scholarly journals Memoirs: The Development of Symbranchus marmoratus

1913 ◽  
Vol s2-59 (233) ◽  
pp. 1-51
Author(s):  
MONICA TAYLOR
Keyword(s):  
Hepatic Vein ◽  
Alimentary Canal ◽  
Vascular System ◽  
Vena Cava ◽  
The Body ◽  
Pyloric Caeca ◽  
Pectoral Fins ◽  
The Third ◽  
Mature Brain ◽  
The Brain

(A) General Features of Development. (1) The egg of Symbranchus is small, its development typically Teleostean and rapid, the larva hatching out in about seven days at a tropical temperature. (2) A rostrum appears just before the larva hatches, increases in size, attains a maximum length of about 1 mm. when the creature is 7 mm. long, decreases in size, gradually dying down to a rounded pad, and eventually disappears just before tbe adult stage is reached. (3) The larva possesses pectoral fins and the shoulder girdle persists in the adult. These fins appear early, are muscularised by the first three trunk myotomes and innervated by the first three spinal nerves. They develop rapidly, reach their maximum size seven or eight days after hatching, shrivel somewhat, and then drop off bodily at Stage 34. The pectoral fins are mainly respiratory organs and possess a rich network of capillaries. There are three principal blood-streams in the fins--one central, afferent, two marginal, efferent. The establishment of perfect branchial respiration is coincident with the falling off of the fins, i. e. when the creature is ten days old. (4) No trace of pelvic fins has been found. (5) Perforated gill-slits of the Elasmobranch type do not occur in early stages, the clefts only becoming perforate after they are covered by the operculum. When branchial respiration is just beginning the gill-chamber opening is a single crescent-shaped one; as development proceeds the anus of the crescent are gradually obliterated, owing to the fnsion of the backwardly growing operculum with the body-wall, and a single median ventral opening is the result. (6) There is a blind diverticulum in the dorsal roof of the mouth behind the hyoid. (B) Alimentary Canal. (1) The alimentary canal has a typical Teleostean character and development, is solid at first, hollowed out secondarily, and has no obvious connection with the yolk. (2) No air-bladder has been detected at any stage. (3) The pyloric valve arises by outpushings of the intestine. These blind cæcal outgrowths have the appearance of very short rudimentary pyloric cæca. (4) Apart from these structures there are no pyloric cæca. (5) The pancreas is an elongated compact gland arising from a dorsal and two ventral rudiments. (6) The liver is elongated and unilobed. (7) There is a typical thymus arising from clefts 2, 3, 4 and 5. (8) A thyroid arises as a solid median derivative of the floor of the pharynx. It is elongated and bilobed anteriorly. (9) The spleen develops early, is very conspicuous, and multilobed at first. (c) Renal Organs. (1) The pronephric chamber and tubule are formed from the nephrotome of the third trunk myotome. (2) There is no communication at any time between splanchnocœle and nephrocœle of the pronephros. (3) The archinephric duct is formed from the nephrotomes of the segments posterior to the third; the conversion of these nephrotomes into a duct takes place simultaneously, involving no backward growth of the archinephric duct. (4) The pronephros is still present in the oldest larva examined. (5) Mesonephric tubule-rudiments appear in Stage 29. They occur from about Segment 25 to Segment 43. Bach arises as a rounded clump of darkly stained cells in the immediate neighbourhood of the archinephric duct. This rudiment is gradually moulded into a twisted tubule, one end of which becomes converted into a Malpighian capsule of the usual type, the other end acquiring an opening into the archinephric duct. (6) There are no peritoneal funnels. (7) Secondary mesonephric tubules arise in connection with the archinephric duct and with the primary mesonephric tubules. These are not fully differentiated in the oldest larva examined. (8) The anterior much-coiled part of the archinephric duct, as well as the mesonephros, is surrounded by pseudolymphatic tissue. (D) Vascular System. (1) The development of the heart and vascular system agrees generally with that described for other Teleosteans. (2) The free anterior part of the left posterior cardinal disappears, the large right posterior cardinal conveying the blood of the inter-renal vein to the heart. (3) There is a close connection between the blood-vessels of the hinder ends of the kidney and liver recalling the posterior vena cava of Polypterus. (4) The subintestinal vein, the front end of which is the vitelline vein of the earlier stages, persists in the adult as a hepatic vein. This hepatic vein joins up with the left anterior cardinal and left jugular to form the left ductus Cuvieri. The right ductus Ouvieri shows no special peculiarity. (E) Nervous System. (1) The brain is at first solid and is hollowed oat secondarily. (2) Three main divisions of the brain can be distinguished in Stage 21. (3) There is tio cranial flexure until Stage 24, and therefore no reason for assuming that the iufundibulum is the morphologically anterior end of the brain. (4) Sagittal sections through the brain at different stages show the usual Teleostean characters. (5) The cerebellum is late in developing and goes on growing after metamorphosis. (6) The optic lobes of the mature brain are relatively smaller than in the developing one. The mid-brain of the adult is the least conspicuous part. (7) The mature brain is elongate, as also are the olfactory and optio nerves, the divisions well separated off.

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