605 



lack of uniformity in the migration paths of the sex-cells, even in re- 

 presentatives of the same vertebrate class. Dodds ('10) has shown that 

 the sex-cells of the teleost Lophius are first found in the mesoblastic 

 somites, whence they later migrate into the lateral plates of mesoderm. 

 These are taken merely as illustrations to show the varied character of 

 their origin and migration path. Dustin in his own work has not been 

 able to show a uniformity of plan in the migration path of the sex- 

 cells of Triton and Chrysemys. One might explain the existence of the 

 stage of the unpaired sex-cell mass by the fact that it occurs at the 

 time when the mesentery is being formed. In such forms as Chrysemys, 

 Lepidosteus, etc., the sex-cells can pass to the sex-gland anläge only 

 by passing up the mesentery as it develops. In other cases, as in 

 Triton and Necturus, they are brought together from each side to meet 

 in the center merely because they occupy the medial edges of the lateral 

 plates, which of necessity bring them together by joining to form the 

 mesentery. 



It appears that the sex-cells arise in the entoderm in the majority 

 of forms and in the mesoderm in others, but the only general laws that 

 I, for one, feel willing to formulate, are that they retain their embryonic 

 characters long after the other cells of the embryo have become spe- 

 cialized, and that they migrate for greater or less distances to the sex- 

 gland anlagen. I can not feel that the migration path is of any general 

 morphological significance in the vertebrates as a whole, but I do be- 

 lieve that a given migration path may be found to apply to certain 

 groups, such as classes, sub-classes, and orders. 



Dustin further claims that I have not noticed the fact that the 

 sex-cells are aggregated into masses during early stages. This I did 

 describe as follows : 



,,In the embryo of 1,7 mm. total length, the sex-cells form loose clusters, as 

 seen in transverse section, and show an amoeboid form. They have begun to mi- 

 grate between the other entoderm cells toward the median line in their journey to 

 the sex-gland anlagen." Anat. Anz., Bd. 29. 



Dustin also takes me to task for not stating that the sex - cell 

 clusters, mentioned in the above quotation , form thickenings of the 

 entoderm. In Eig. 2 of my paper, it can be seen that the somewhat 

 scattered sex-cells, of the 2,8 mm. stage there shown, occasion a thick- 

 ening of the entoderm. Unless one were afflicted with what our German 

 friends call "Spitzfindigkeit", he could readily appreciate the fact that 

 the loose masses mentioned in the quotation just given would occasion 

 a decided thickening. I most clearly recognized these thickenings and 

 the sex-cells that caused them. 



In one point, Dustin has found a feature that I did not mention 

 in my paper, namely, that, in some specimens, one finds, at times, a few 

 sex-cells that have migrated up into the splanchnopleure. He is quite 

 welcome to the credit for this discovery, although I had observed it a 

 number of times in my early work, but was not sufficiently impressed 

 with its importance to make special mention of it in a paper intended 

 as a preliminary survey. 



We may now pass from these less important points of difference. 



