The Animal Organism and its Germ-Layers 73 



a part of the germ-layer theory, it is a great gain to have 

 perceived clearly that it is in tlie layered stage of the in- 

 dividual's life in many species that the next generation of 

 individuals takes its rise. However, it does not by any 

 means follow that because the sex-cells are born, as one 

 might say, at this early time in the life of the parent, they 

 are fully exempt from parental influence during all the per- 

 iod intervening between the layered stage of the parent and 

 its stage of sexual maturity, that is, of final separation and 

 extrusion of the sex-cells. 



It seems to me the fact that the sex-cells of even some 

 vertebrates are found at an early stage of embryonal life 

 (•mbedded in one or another of the germ-layers at points far 

 removed from where the definitive germ glands will later ap- 

 pear, may signify just such influence. In other words, it 

 may be the meaning of the "precocious segregation," as it is 

 called, of germ-cells ought to be taken along with their wide 

 dissemination in the embryo, and interpreted as speaking 

 against and not for the fundamental isolation of the germ- 

 plasm. 



The distribution of sex-cells in the early embryos of ver- 

 tebrates has been studied by several zoologists, among them 

 being C. H. Eigenmann and B. M. Allen. Allen's investiga- 

 tions are specially important because of their wide com- 

 parative scope. In The Origin of the Sex-Cells of Amia and 

 Lepidosteus he gives a set of useful diagrammatical com- 

 parative drawings showing the mode of origin of the sex- 

 cells from the endoderm of a reptile {Chrysomys)^ an am- 

 ])hibian (Frog), and two fishes {Amia and Lepidosteus) , but 

 reaffirms in his discussion the result that the cells arise in 

 the mesoderm in the tailed amphibians. 



