Ontogenetic and Phylogenetic Variation of Form and Function of the Ocular Lens

1989 ◽  
Vol 174 ◽  
Author(s):  
J. G. Sivak
Keyword(s):  
Refractive Index ◽  
Life Histories ◽  
Spherical Aberration ◽  
Focal Length ◽  
Relative Size ◽  
Crystalline Lens ◽  
Optical Quality ◽  
Form And Function ◽  
And Function ◽  
Optical Structure

AbstractThe crystalline lens of the eye is a unique optical structure that continues to develop within the eye throughout life. This process of development results in the formation of a lens with a gradient refractive index that has important optical consequences, particularly in the control of spherical aberration. The optical characteristics of the vertebrate crystalline lens are reviewed in terms of environmental concerns and spherical aberration. Lens shape and relative size are determined by such factors as whether the eye is to be used in air or water and whether it is to be used under scotopic or photopic conditions. The continued growth of the lens through life can be related to whether the lens exhibits positive or negative spherical aberration. In general, spherical aberration, as measured using a split laser beam method with excised lenses, is minimized in species with life histories indicating superior resolution ability. In addition, lens optical quality, as indicated by zonular differences in focal length, deteriorates with lens age. While the embryonic and post-embryonic lens undergoes significant change in size, shape and refractive index distribution, it appears that focal constancy is maintained, at least in certain species. This finding may indicate a means of simplifying the process of emmetropization.

Seasonal reproductive anatomy and sperm storage in pleurocerid gastropods (Cerithioidea: Pleuroceridae)

2014 ◽  
Vol 92 (12) ◽  
pp. 989-995 ◽  
Author(s):  
Nathan V. Whelan ◽  
Ellen E. Strong
Keyword(s):  
Seasonal Variation ◽  
Life Histories ◽  
Gross Anatomy ◽  
Egg Laying ◽  
Conservation Strategies ◽  
Freshwater Species ◽  
Form And Function ◽  
Reproductive Anatomy ◽  
And Function ◽  
And Behavior

Life histories, including anatomy and behavior, are a critically understudied component of gastropod biology, especially for imperiled freshwater species of Pleuroceridae. This aspect of their biology provides important insights into understanding how evolution has shaped optimal reproductive success and is critical for informing management and conservation strategies. One particularly understudied facet is seasonal variation in reproductive form and function. For example, some have hypothesized that females store sperm over winter or longer, but no study has explored seasonal variation in accessory reproductive anatomy. We examined the gross anatomy and fine structure of female accessory reproductive structures (pallial oviduct, ovipositor) of four species in two genera (round rocksnail, Leptoxis ampla (Anthony, 1855); smooth hornsnail, Pleurocera prasinata (Conrad, 1834); skirted hornsnail, Pleurocera pyrenella (Conrad, 1834); silty hornsnail, Pleurocera canaliculata (Say, 1821)). Histological analyses show that despite lacking a seminal receptacle, females of these species are capable of storing orientated sperm in their spermatophore bursa. Additionally, we found that they undergo conspicuous seasonal atrophy of the pallial oviduct outside the reproductive season, and there is no evidence that they overwinter sperm. The reallocation of resources primarily to somatic functions outside of the egg-laying season is likely an adaptation that increases survival chances during winter months.

The visual system and paleoecology of the Silurian ostracod Primitiopsis planifrons

2009 ◽  
Vol 83 (3) ◽  
pp. 414-421 ◽  
Author(s):  
Gengo Tanaka ◽  
David J. Siveter ◽  
Andrew R. Parker
Keyword(s):  
Visual System ◽  
Water Depth ◽  
Spherical Aberration ◽  
Focal Length ◽  
Relative Size ◽  
Spherical Mirror ◽  
Subtidal Zone ◽  
Ontogenetic Change ◽  
Geological Evidence ◽  
Independent Test

Here we report the first detailed reconstruction of the eye and visual system of a Paleozoic ostracod, namely the dimorphic primitiopsid (Palaeocopa) Primitiopsis planifrons Jones, 1887. Evidence from the cuticular lens morphology and its position on the valve suggests that P. planifrons had a naupliar eye, which is the most common optical system in crustaceans. the characters of the eye, such as the separated cuticular lens on each valve and the strongly calcified nature of the lens and its diameter, are concordant with that of some Recent podocopid ostracods in which a divided type of naupliar eye is present. Ray tracing of the reconstructed cuticular lens of the primitiopsid species demonstrates strong spherical aberration and a very long focal length (as in the eye of podocopids), which implies the presence of a spherical mirror (tapetum) below the lens. Study of the ontogenetic change of the valve thickness aids the suggestion that P. planifrons was nektobenthic. the size of its cuticular lens in relation to that of living podocopid ostracods, and the water depth at which these Recent forms occur, indicates that P. planifrons may have lived in a relatively shallow, well lit environment such as the deep subtidal zone. These interpretations are consistent with supposed paleoenvironmental conditions derived from geological evidence. Thus, analysis of the nature and relative size of the eye gives an independent test to help identify paleoenvironmental parameters of long extinct ostracods.

The Relationship of Form and Function of Minute Characters of Lepidopterous Larvae, and its Importance in Life-History Studies

1964 ◽  
Vol 96 (7) ◽  
pp. 991-1004 ◽  
Author(s):  
Margaret Rae MacKay
Keyword(s):  
Life History ◽  
Chemical Control ◽  
Life Histories ◽  
The Other ◽  
Taxonomic Study ◽  
Form And Function ◽  
Morphological Studies ◽  
And Function ◽  
Relationship Of ◽  
The Relationship

AbstractThe information to be obtained from thorough life-history studies is an extremely useful tool, perhaps especially so when ecology is being emphasized, as it is to-day, by the life-table and other mathematical approaches to the study of population processes. This information is desired by workers in many fields of entomology – by the biological and chemical control experts, the biomathematicians, the theorists and even the taxonomists. However, much of the knowledge that these workers require, for instance the fine distinctions of behaviour and environment, has been overlooked in most life-history studies, and I strongly suspect that one of the weaknesses of studies of this nature has been the failure to analyse the mode of living of an insect (or, in the case of Lepidoptera, of the immature forms) in relation to the anatomy on one hand and environmental circumstances on the other. To look for these relationships, I believe that one requires (a) the ability and perseverance to perceive detail as minute as that required for a taxonomic study, and (b) a considerable knowledge of the taxonomic detail that is to be obtained from basic morphological studies. Therefore, in this paper, attention is drawn to pertinent structural characters of lepidopterous larvae and their probable connection with the behaviour and microhabitats of the larvae, in the hope that some guidance may be offered to future students of life-histories, at least in Lepidoptera.

scholarly journals Contribution of the gradient refractive index and shape to the crystalline lens spherical aberration and astigmatism

2013 ◽  
Vol 86 ◽  
pp. 27-34 ◽  
Author(s):  
Judith Birkenfeld ◽  
Alberto de Castro ◽  
Sergio Ortiz ◽  
Daniel Pascual ◽  
Susana Marcos
Keyword(s):  
Refractive Index ◽  
Spherical Aberration ◽  
Crystalline Lens ◽  
Gradient Refractive Index

scholarly journals Rules and principles for determining the dispersive ratio of glass; and for computing the radii of curvature for achromatic object glasses, submitted to the test of experiment

1833 ◽  
Vol 2 ◽  
pp. 316-317
Keyword(s):  
Refractive Index ◽  
Spherical Aberration ◽  
Focal Length ◽  
Refractive Indices ◽  
Practical Application ◽  
Convex Lens ◽  
Astronomical Instruments ◽  
Rules And Principles ◽  
The Subject ◽  
Source Of Error

The author begins this paper by an enumeration of the various works on the subject extant in our language, and a general mention of the writings of foreign mathematicians, which he considers as leaving room for further inquiry and simplification. He then states the method employed in his experiments for determining the refractive and relative dispersive powers of his glasses, the former of which is that generally known and practised;—of measuring the radii and focal length of a lens, and thence deriving the refractive index; with some refinements in its practical application, consisting chiefly in using the lens as the object-glass of a telescope, and adapting to it a positive eye-piece and cross-wires, which are brought precisely to the true focus by the criterion of the evanescence of parallax arising from a motion of the eye, as is practised in adjusting the stops of astronomical instruments. The only source of error it involves is in the measurement of radii of the tools which it was found could always be performed within 1/500th of their whole values. The dispersive ratio of two glasses was determined by over-correcting the dispersion of a convex lens of the less dispersive glass by a concave of the greater, and then withdrawing the latter from the former till the achromaticity is perfect, or as nearly so as the materials will admit, and measuring the interval between the lenses and their foci, from which data the ratio of their dispersive powers is easily obtained. The refractive indices and dispersive ratio thus determined, the next step is to find the radii of curvature so as to destroy spherical -aberration. In this investigation, the author does not consider it as necessary to limit the indeterminate problem by any further condition, as others before him have done, but regarding it as a matter of great convenience to avoid contact of the interior surfaces in the centre of the glasses, leaves it open to the optician to make a choice within certain limits, thus avoiding what he considers as an intricate equation arising out of the fourth condition. He proceeds, therefore, to express analytically the aberrations of the glasses, and to deduce the equation expressive of its destruction, which of course involves one indeterminate quantity; this may be either of the radii, or any combination of them. The author chooses the ratio of the radii of the interior and exterior surfaces of his flint lens for this indeterminate, which he assumes, as well as may be, to satisfy the condition of the absence of contact and near equi-curvature of the adjacent surfaces; thence deduces, first, the radii of both of the surfaces of the flint lens; next, its aberration to be corrected; and thence, by the solution of a quadratic, or by the use of a table containing its solutions registered in various states of the data, the ratio of the radii of the convex, whence the radii themselves are easily deduced.

scholarly journals Bioelectric-calcineurin signaling module regulates allometric growth and size of the zebrafish fin

2018 ◽  
Author(s):  
Jacob M Daane ◽  
Jennifer Lanni ◽  
Ina Rothenberg ◽  
Guiscard Seebohm ◽  
Charles W Higdon ◽  
...  
Keyword(s):  
Ion Channel ◽  
Relative Size ◽  
Calcineurin Inhibitors ◽  
Common Mechanism ◽  
Allometric Growth ◽  
Wild Type ◽  
Form And Function ◽  
C Terminus ◽  
And Function ◽  
Calcineurin Signaling

AbstractThe establishment of relative size of organs and structures is paramount for attaining final form and function of an organism. Importantly, variation in the proportions of structures frequently underlies adaptive change in morphology in evolution and maybe a common mechanism underlying selection. However, the mechanism by which growth is integrated within tissues during development to achieve proper proportionality is poorly understood. We have shown that signaling by potassium channels mediates coordinated size regulation in zebrafish fins. Recently, calcineurin inhibitors were shown to elicit changes in zebrafish fin allometry as well. Here, we identify the potassium channel kcnk5b as a key player in integrating calcineurin’s growth effects, in part through regulation of the cytoplasmic C-terminus of the channel. We propose that the interaction between Kcnk5b and calcineurin acts as a signaling node to regulate allometric growth. Importantly, we find that this regulation is epistatic to inherent mechanisms instructing overall size as inhibition of calcineurin is able to bypass genetic instruction of size as seen in sof and wild-type fins, however, it is not sufficient to re-specify positional memory of size of the fin. These findings integrate classic signaling mediators such as calcineurin with ion channel function in the regulation of size and proportion during growth.

Resolution Attainable With the Present Day STEM

1973 ◽  
Vol 31 ◽  
pp. 230-231 ◽  
Author(s):  
J. S. Wall ◽  
J. P. Langmore ◽  
H. Isaacson ◽  
A. V. Crewe
Keyword(s):  
Spherical Aberration ◽  
Focal Length ◽  
Incident Beam ◽  
Scanning Transmission Electron Microscope ◽  
Aperture Size ◽  
Magnetic Lens ◽  
Peak Intensity ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Half Angle

The scanning transmission electron microscope (STEM) constructed by the authors employs a field emission gun and a 1.15 mm focal length magnetic lens to produce a probe on the specimen. The aperture size is chosen to allow one wavelength of spherical aberration at the edge of the objective aperture. Under these conditions the profile of the focused spot is expected to be similar to an Airy intensity distribution with the first zero at the same point but with a peak intensity 80 per cent of that which would be obtained If the lens had no aberration. This condition is attained when the half angle that the incident beam subtends at the specimen, 𝛂 = (4𝛌/Cs)¼

Improvements in the electron probe forming capabilities and x-ray hole counts in the Philips TEM

1983 ◽  
Vol 41 ◽  
pp. 376-377
Author(s):  
Richard L. McConville
Keyword(s):  
Field Strength ◽  
Electron Probe ◽  
Spherical Aberration ◽  
Focal Length ◽  
Objective Lens ◽  
Parallel Beam ◽  
Tilt Axis ◽  
X Ray ◽  
Small Probe ◽  
Specimen Height

A second generation twin lens has been developed. This symmetrical lens with a wider bore, yet superior values of chromatic and spherical aberration for a given focal length, retains both eucentric ± 60° tilt movement and 20°x ray detector take-off angle at 90° to the tilt axis. Adjust able tilt axis height, as well as specimen height, now ensures almost invariant objective lens strengths for both TEM (parallel beam conditions) and STEM or nano probe (focused small probe) modes.These modes are selected through use of an auxiliary lens situ ated above the objective. When this lens is on the specimen is illuminated with a parallel beam of electrons, and when it is off the specimen is illuminated with a focused probe of dimensions governed by the excitation of the condenser 1 lens. Thus TEM/STEM operation is controlled by a lens which is independent of the objective lens field strength.

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