396 



set taking intermediate rank between the extremes. The relative 

 number of sex-cells might be determined by congenital causes, or less 

 probably by the part of the breeding season at which the eggs are 

 laid, or by other causes. It is useless to speculate upon this question 

 in the absence of fuller data. One thing, however, is very certain : 

 that is, that these differences in the number of sex-cells are not due 

 to differences in the stage of development. 



Both Eigenmann and Beard have shown that the distribution of 

 the sex-cells may be very irregular. I find this quite true in all 

 stages of Chryserays studied. In the stages before the sex-cells have 

 migrated into the sex-glands, there is often a very great preponderance 

 in the number of sex-cells on one side over that of the other. No. 14 

 is the most extreme case noted, although No. 13 is almost as striking. 

 In one, the preponderance is upon the right side, while in the other it 

 is upon the left. These two embryos came from the same nest, lu 

 other cases, as No. 5, the number is more nearly equal. 



During the migration of the sex-cells, many lag hopelessly behind, 

 while others go astray. Their final distribution is very different in 

 different specimens. Upon an average, 47,7 % finally reach the sex- 

 glands, while the remainder come to rest in the alimentary tract, the 

 mesentery, and the region between the root of the mesentery, the 

 aorta, and the mesonephroi. This region includes the adrenal Anlagen. 

 The term Adr. in our table is applied to it. The percentage of sex- 

 cells reaching the sex-glands may vary all the way from 24 % to 

 71 %. There is a general correspondence in the number of sex-cells 

 in the two sex-glands, the average being 255 + ^or the right one, 

 and 231 for the left. The number may range from 78, m embryo 20, 

 to 357, in embryo 31, and even to 601, in embryo 22. It is barely 

 possible that there has been a slight amount of multiplication in the 

 sex-cells of the last named embryo. If such be the case, it would 

 exhibit very great precocity in this regard. The only evidences of 

 such division are found in the presence of a few small sex-cells which 

 appear to occur in pairs. They are, however, no larger than those 

 of the earlier stages, their sister cells having in the meantime in- 

 creased in size. There are no direct indications of cell division, nor 

 does the total number of sex-cells of the embryo reach that of some 

 other specimens in which there has most certainly been no division 

 of them. The extreme of asymmetry is found in embryo 25, where 

 there are 239 sex-cells in the right sex-gland, as compared with 161 

 in the left. A glance at the table of results will show very great 

 differences in the number of sex-cells that come to rest in the various 



