Embryogenesis of an Invertebrate Lymphoid Organ: The Asterina Gibbosa Axial Organ (Asterids, Echinodermata)

The metamerization of the coelom leads to the axial complex genesis. Mesodermic cells appear besides the stone canal (larva 12 days old): they constitute the axial organ (AO) which develop, in the ventral side, the oral part (PO). This last part corresponds (sensu stricto) to the ancestral lymphoïd organ.

Memoirs: The Reproductive System and Associated Organs of the Brittle-Star Ophiothrix Fragilis

1. The organs associated, either directly or indirectly, with reproduction in the Ophiuroidea are the axial organ and related sinuses (axial organ complex), the genital raehis, the gonads (localized expansions of the raehis), the gonoducts, and the genital bursae. 2. Evidence is presented in favour of the view of Fedotov (1924) that the axial organ of Ophiuroids is made up of two closely associated parts each surrounded by its own sinus from the wall of which it is, during development, proliferated. The left axial sinus (aboral in the adult) is derived from the left anterior coelom of the larva, the right axial sinus (oral in the adult) from the madreporie vesicle which itself is a derivative of the right anterior coelom of the larva. 3. The ampulla of the stone canal is continuous with, and is part of, the left axial sinus. 4. An account is given of the morphology and histology of the genital rachis and sinus. 5. Examination of the gonads of female Ophiothrix indicate that the breeding season extends from about March to October and that, during this time, there is periodic emission of ova, probably at monthly intervals. Males, on the other hand, produce sperm all the year round. 6. The genital bursae number two pairs to each interradial pouch. They serve, primarily, as organs of respiration. Special mechanisms, which are described, are concerned in the intake and expulsion of water. 7. The gonads do not discharge their products directly into the genital bursae nor through temporarily formed pores in the body-wall but through specially developed and permanent gonoducts, one to each of the ten gonads. 8. Young specimens found in the genital bursae have attained their position only after a period of free-swimming larval life. After settling and metamorphosing, some of the young individuals crawl into the bursae. 9. As a consequence of the previous observation it is pointed out that the presence of the young within the genital bursae of the adult is by no means an indication of a viviparous habit.

Reversal of asymmetry in the plutei of Echinus miliaris

While engaged in artifical rearing of Echinus miliaris under the guidance of Prof. MacBride, I have come across a number of abnormal plutei which had the hydrocœle developed on the right side instead of in its normal position on the left side. Such reversed larvæ were first found on May 31, 1920, when they were eleven days old (text-fig. 1). The “larval” body was quite normal both in size and shape, but the hydrocœle, stone-canal, axial sinus, madreporic vesicle, and amniotic invagination were all situated on the right side, so that the larva became a perfect mirror-image of the normal larva. Such larvæ developed further with exactly the same rate of growth as the normal ones, an echinus-rudiment being well developed on the right side, until at last, when a month old, some few of them passed metamorphosis. The young urchins (text-fig. 2) showed no features visible externally which differed from those of urchins metamorphosed from normal larvæ. A similar case has previously been described only by Runnström in two individuals found among artifically reared larvæ of Strongylocentrotus lividus ((9), pp. 2–3, 7–10; (12), pp. 419–24, Plate 14, figs. 12–16). In other classes of Echinoderms, auriculariæ with the hydrocœle on the right side were noticed by Müller many years ago ((7), pp. 101, 109; Plate 5, fig. 1), and a similar state of affairs in two plutei of Ophionotus hexactis has recently been discovered by Mortensen. In both these case the abnormal larvæ were found in nature, not reared under artificial conditions. The purpose of our experiments was to repeat Prof. MacBride’s method of artifical production of the double hydrocœle (6). Having been unable to get an uninterrupted supply of enough food, which consisted of Nitzchia , and from other causes unknown to us at present, we could not arrive at any satisfactory conclusion so far as the effect of the increased salinity is concerned. From both lots of cultures, treated with the “hypertonic” sea water as well as untreated, more than 10 per cent. of the larvæ exhibited the situs inversus, and much less number, 2 per cent. at most, developed the double hydrocœle.

Memoirs: Planktothuria diaphana, gen. et sp. n

1. A medusa-like Holothurian has been found off the South African coasts. 2. It is devoid of external podia. 3. Podia are found embedded in the thick gelatinous epidermis, and are arranged in three groups in the form of-- (1) Arms or oral podia forming a hood-like structure over the mouth, and supplied from the dorsal and ventrolateral radial canals. (2) Dorsal podia, which are slender and terminate in knobs. (3) Lateral podia towards the posterior end of the body. 4. Tentacles are supplied by the circular canal. 5. The stone-canal is single, and opens to the exterior by a single opening. 6. Calcareous deposits do not appear to occur in any part of the body, except in the form of small knobbed spheres round the oesophagus. 7. Respiratory tree and Cuvierian organ absent. 8. Gonads in two grape-like masses, one on each side of the dorsal mesentery, and opening to the exterior by a long, slender duct. Mature ova .3 mm. in diameter, and provided with, oil-globules. 9. It cannot be placed, in any of the known groups of Holothurians, chiefly on account of the origin of the tentacles from the circular canal.

Memoirs: The Development of the Genital Organs, Ovoid Gland, Axial and Aboral Sinuses in Amphiura squamata; together with some Remarks on Ludwig's Hæmal System in this Ophiurid

The most important results detailed in this paper are as follows: 1. The primitive germinal cells are peritoneal. 2. The ovoid gland is a solid organ, which develops from aportion of the rudiment which gives rise to the primitive germinal cells. 3. The axial and aboral sinuses are involutions of the cœlom, and have no connection with the ampulla of the stone canal or each other. 4. The genital rachis is an outgrowth from the ovoid gland into the aboral sinus, the formation of sinus and rachis proceeding together. 5. There is no evidence of the existence of Ludwig's hæmal system in Amphiura squamata. 6. Both kinds of cells, germinal and interstitial, which are found in the genital rachis, are formed in the ovoid gland. 7. The germinal cells are formed from peritoneal cells directly; there is no evidence of the transformation of the special cells of the ovoid gland into Urkeimzellen.

II. Note on the madreporite of cribrella ocellata

I have a series of vertical longitudinal (radial) sections carried through the madreporite, &c., of a full-grown specimen of Cribrella ocellata : in this series the madreporic canals have a peculiar relation to the stone canal or water-tube.