The formation of the germ-layers in crangon vulgaris / by W.F.R. Weldon.

  • Weldon, W. F. R. (Walter Frank Raphael), 1860-1906.
Date:
[between 1890 and 1899?]
Catalogue details

Licence: Public Domain Mark

Credit: The formation of the germ-layers in crangon vulgaris / by W.F.R. Weldon. Source: Wellcome Collection.

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    captivity being rendered useless by the great abundance of material procured for me by the fishermen of the Association. The gravid females were killed by immersion in a solution of corrosive sublimate, warmed to about 50° C., and were after- wards treated with increasingly strong alcohol in the usual way. The shells were easily removed from the eggs with needles; and the eggs themselves were stained, either with picrocarmine in the case of those intended for sections, or when intended for surface views with Grenacher’s alum- carmine. The youngest eggs observed were already divided super- ficially into four equal segments. The egg at this stage is somewhat elliptical, having a long diameter of 0°5 mm., a short diameter of 0'4 mm. It is surrounded by a single, delicate, transparent shell-membrane, which is, as pointed out by Kingsley, completely filled by the living egg. The appearance of the hardened egg, after removal of the shell, is seen in fig. 1, where the whole surface of each blastomere is seen to be crowded with small spherules of yolk. This spherical con- dition of the yolk-particles was well retained in all my speci- mens, though Kingsley appears to have found that the yolk spherules broke up and ran together into masses during the process of hardening. The yolk spheres are so densely crowded on the surface that the nuclei cannot at this stage be rendered visible in the uninjured egg. In sections a single nucleus, surrounded by a small mass of protoplasm, is found in the centre of each blastomere. The protoplasmic mass sends processes into the yolk, which can easily be followed for a certain distance; and there can be little doubt that a proto- plasmic reticulum extends between the yolk spherules through the whole substance of each blastomere. Whether a proto- plasmic connection between the adjacent blastomeres is present or absent I have been unable to determine. It is to be noticed that during the stage with four nuclei the segmentation furrows are simple superficial grooves, which do not extend to any considerable distance below the surface of the egg, so that the great mass of the yolk is as yet
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