SEX-CELLS OF AMIA AND LEPIDOSTEUS 25 
to certain cells of the peripheral entoderm. This not only in- 
volves a similarity of the nuclei but of the dimensions of the cell 
bodies. This is true even after the sex-cells and the correspond- 
ing cells of the peripheral entoderm have lost their yolk through 
absorption. ; 
In the stage of 11.4 mm., the yolk mass has been greatly 
reduced (figs. 25 and 26). Only here and there about its periph- 
ery are cells to be found with well defined outlines. The great 
mass is syncytial, with large nuclei of varying size scattered here 
and there. While these nuclei of the vitelline mass are much 
larger than the sex-cell nuclei, they bear a close resemblance to 
the latter. The nuclei of the well defined peripheral cells are prac- 
tically identical in size and appearance with those of the sex-cells. 
While the similarity between sex-cells and between these two 
classes of cells is not so marked in Lepidosteus as in Amia, yet 
it appears to be equally true. In the 17 mm. stage (figs. 14 and 15) 
the yolk mass is still of fair size. There is a layer of peripheral 
entoderm that is largely made up of cells with clear boundaries, 
whose nuclei are similar to those of the sex-cells in respect to the 
presence and character of the plasmosome and in the form and 
distribution of the chromatin material. In many cases these 
nuclei are larger than those of the sex-cells; but many are found 
which are quite as small. These grade into the very large 
nuclei of the syncytial vitelline entoderm. 
At this stage the tissues of the body have taken on their dis- 
tinctive characters and their component cells have undergone in 
many cases a high degree of specialization. This emphasizes 
strongly the similarity between the sex-cells and the cells of the 
peripheral entoderm. 
As we pass back to earlier stages, such as those of 9.3 mm., 
5.9 mm., ete., we still find this similarity between these types of 
cells, although the nuclei of all the body cells tend to show greater 
and greater similarity to one another in the earlier stages. For 
instance, it becomes quite difficult to distinguish the nuclei of the 
gut entoderm cells from those of the sex-cells. Even the nuclei 
of the Wolffian ducts show quite a close resemblance to the sex- 
cell nuclei during the early stages of development. 
