48 HARLEY N. GOULD 



which it is shown that the male, female, and hermaphroditic 

 individuals which occur have chromosomal differences. 



In the plant kingdom two cases, at least, are known where one 

 of the germ cells (the spermatozooid) of hermaphrodite plants 

 is heterozygous for sex, while the other (the ovum) is homozy- 

 gous. This was determined by crossing with dioecious forms 

 (Shull, '14 and Correns, '07). 



Now it is worthy of note that those authors (Ancel and 

 Buresch) who have concluded that the female germ cell is dif- 

 ferentiated out of the indeterminate sex cell as a result of a dif- 

 ferent nutrition from that of the spermatogonia have figured in 

 their plates a rather simple method of differentiation of the 

 oocyte. In their figures of the oogenesis there is no such com- 

 plex series of changes in the nucleus as has been found in Palu- 

 dina by Popoff ('07) , as Demoll has described for Helix pomatia 

 (the same form on which Ancel worked), and as the present 

 writer has seen in Crepidula plana. Demoll, it will be recalled, 

 does not hold to the nutrition theory of germ cell determination. 

 The possibihty occurs to the writer that the early stages of dif- 

 ferentiation of the oocytes might be misinterpreted on account 

 of their resemblance to the primary spermatocytes, in animals 

 where the two existed side by side. 



In every herniaphrodite animal it must be true that at some 

 stage of development there is an indifferent sex cell; for the 

 egg, and the developing embryo, carries within it the potentiahty 

 of developing two kinds of sex elements (Hegner, '14). The un- 

 segmented egg, at least, is an 'indifferent germ cell' as well as an 

 'indifferent somatic cell.' The question with which we are 

 concerned, then, is to find the point at which the male and 

 female elements are separated. It does not seem necessary 

 that this point must always be the same in the life cycle. It is 

 not difficult to believe that in some species male and female ele- 

 ments are but separated during the early embryogeny, and in 

 another that they are contained in the same cell through many 

 cell-generations. It seems to the writer, however, that the now 

 widely spread view that the germ cells of hermaphrodites arise 

 from an actually undifferentiated germinal epithelium, even in 



