SEX-CELLS OF AMIA AND LEPIDOSTEUS Hy 
It will be seen by comparing the figures drawn to scale that the 
mesentery is at this stage not only relatively but actually much 
thicker than it is during later stages. The accompanying table 
serves to show the number of sex-cells and their distribution in 
certain stages. ) 
In this specimen 73 sex-cells have already migrated out of 
the gut entoderm into the surrounding mesoderm tissues. While 
most of them have migrated upward into the loose mesenchyme 
and splanchnopleuric mesoderm of the anlage of the mesentery, 
a few have passed laterally into the portions of the splanchno- 
pleuric mesoderm that enter into the formation of the intestinal 
wall. While the migration of the sex-cells is seen to be well 
under way at this stage, the great majority of them still remain 
in the dorsal portion of the gut entoderm. Very few, indeed, 
are to be found in the ventral half at this stage. The sex-cells 
of the gut entoderm are easily distinguishable from the other 
entoderm cells; the latter have lost very nearly all of their yolk 
material and have become cylindrical in shape. These features 
stand out in sharp contrast to the large yolk content and spherical 
form of the sex-cells. 
The migration of sex-cells from the gut entoderm into the 
mesenchyme dorsal or lateral to it may be clearly seen at a few 
points, as illustrated in figs. 7 and 8. They retain for the most 
part their spherical form, but cases like that shown in fig. 7 
can be readily found. The shape of this sex-cell clearly indicates 
the mode of progression. They, undoubtedly, pass through the 
loose network of mesenchyme by an amoeboid movement, how- 
ever slow or intermittent it may be. 
In this stage sex-cells are found in the hind gut from its cranial 
end to within .2 mm. of the cloaca, a distance of 2.6 mm. 
Lepidosteus 9.2 mm. long. The number of sex-cells that have 
migrated out of the gut entoderm is 136 in this specimen. The 
number of these is still increasing but solely by migration from 
the entoderm, since there is no evidence of division of the sex- 
cells during these stages of sex-cell migration. 
In this stage the coelomic cavities have appeared in the dorsal 
portion of each lateral mesodermal plate and the mesentery is 
