HEREDITY AND ENVIRONMENT 187 



we have a definite descent of the sperm cell in at 

 least four stages : (i) Division of living epithelium cell 

 into two cells, one of which becomes a spermatogen and 

 passes into the second layer, while the other does not 

 migrate, but enlarges and becomes a sustentacular 

 cell, apparently connected with the nutrition of the 

 spermatozoa when fully formed and during conversion. 

 (2) Division of the spermatogen. (3) Further division 

 and resulting daughter cells are converted into spermato- 

 blasts. (4) Growth and elongation of spermatoblasts 

 into spermatozoa. 



In the ovaries similar processes appear to take 

 place by which the follicles are developed from lining 

 epithelium. Some of the cells develop into ova, and 

 are thus direct descendants of epithelium. So far it 

 seems that there is no reason whatsoever to be found 

 in any of the processes for assuming that germ-plasm 

 in the narrow sense exists at all. The succeeding 

 phenomena can be accounted for without any great 

 exercise of faith if we consider such processes as de- 

 pendent on the cell's energy and the catalysts, or tools, 

 brought over in the oocyte and sperm cell, or derived 

 later by the zygote from the tissues and blood-stream 

 of the maternal parent. For during the most important 

 part of the reproductive cell's life, that spent in the 

 originating tissue, it was a unicellular organism acquir- 

 ing the characteristics which under other conditions 

 develop and diverge. If such a view is accepted the 

 great determining period of the reproductive cell is its 

 early testicular or ovarian history, not that of its 

 later embryonic life. During the first state we can 

 easily imagine the epithelioid cell acquiring freely the 

 activators, catalysts, or similar hormones, which direct 



