The presence of these seems to shew that the molecular cohesion of the protoplasm becomes, as compared with other parts, much diminished in the region where a furrow is about to appear, so that before the protoplasm finally gives way along a particular line to form a furrow, its cohesion is broken at numerous points in this region, and thus a series of vacuole-like spaces is formed.
If this is the true explanation of the formation of these spaces, their presence gives considerable support to the views of Dr Kleinenberg upon the causes of segmentation, so clearly and precisely stated in his monograph upon Hydra; and is opposed to any view which regards the forces which come into play during segmentation as resident in the nucleus.
I have not observed the peculiar threads of protoplasm which Oellacher[106] describes as crossing the commencing segmentation furrows. I have also failed to discover any signs of a concentration of the yolk-spherules, round one or two centres, in the segmentation spheres, similar to that observed by Oellacher in the segmenting eggs of Osseous Fish. The appearances observed by him are probably connected with the behaviour of the nucleus during segmentation, and are related to the curious bodies I have already described.
With reference to the nuclei which Oellacher[107] has described as occurring in the eggs of Osseous Fish during segmentation, there can, I think, be little doubt that they are identical with the peculiar nuclei in the Elasmobranch eggs.
In an unsegmented germ there occurred at a certain point in the section ... a small aggregation of round bodies. I do not feel satisfied whether these aggregations represent one or more nuclei.
Fig. 29 shews such aggregation; by focusing at its optical section eleven unequally large rounded bodies measuring from 0.004 - 0.009 mm. may be distinguished. They lay as if in a multilocular gap in the germ mass, which however they did not quite fill. In each of these bodies there appeared another but far smaller body. These aggregations were distinguished from the germ by an especially beautiful intense violet gold chloride colouration of their elements. The smaller elements contained in the larger were still more intensely coloured than the larger.