392 



number and arrangement are not considered to have any particular 

 significance, being attributed to individual variation. Beard ('02), 

 on the other hand, sees a deep significance in the number of sex-cells. 

 Since his whole work upon this subject is colored by his theory of 

 the phorozoon or asexual generation, we shall briefly outline that 

 theory, or rather, hypothesis. According to his view, the blastoderm, 

 prior to the period when the embryo begins to appear, corresponds 

 to the sporophyte of plants. To it he gives the term phorozoon. 

 Soon, one of its cells begins to undergo a definite number of divi- 

 sions, which result in producing the primary germ-cells. The number 

 of these may be great or small, according to the species of the animal. 

 One of these sister cells develops to form the embryo into which the 

 other primary germ-cells migrate. The germ-cells or sex-cells are 

 then each coordinate with the embryo. The number of primary sex- 

 cells found in any species would be represented by 2" — 1. Beard 

 found that the female embryos of Raja batis contained approximately 

 511 primary sex-cells, while the embryos destined to become males 

 contained about 255. Hence, within this species, each sex is distin- 

 guished by its characteristic number of primary sex-cells. No sex 

 differences of this kind were found in the other species studied. 



Considerable fluctuations from the theoretical number assumed 

 by Beard are found in his lists of results. For instance, specimens 

 of Pristiurus melanostomus, with a theoretical number of 127 primary 

 sex-cells, are shown by his counts to have from 100 to 153. Beard 

 explains this variation upon the ground of degeneracy, in the one case, 

 and of twice counting the same cells in the other. He explains that 

 some cells larger than the primitive sex-cells may not have undergone 

 their final division or divisions in the course of reaching the stage of 

 primitive sex-cells. 



Whatever differences there are between these two authors, both 

 agree (1) that for a long period in the early development of the em- 

 bryo, the sex-cells do not divide, the number remaining constant save 

 for the degeneration of a very few, and (2) that some come to lie in 

 places outside of the sex-glands. Beard lays more particular stress 

 upon this point in support of his hypothesis, to the efiect that cancer 

 is caused by the development of these abnormally situated sex-cells 

 into abortive embryos. 



In making the counts of sex-cells recorded in this paper, a cer- 

 tain margin of possible error must be allowed. This must be fairly 

 large in the early stages, embryos of a total length of 2,8 mm to a 

 length of 5 mm, as measured from the cervical bend to the tail bend. 



