animals the primordial germ-cell appears later, after the first 

 few divisions of the ovum, during or after the embryogen- 

 esis. Many facts now support the theory {Evolution Theory, 

 Vol. l,pp. 410-411). Jager and Messbaum had practically 

 come to the same conclusion earlier for they had observed 

 that at an early stage in the embryo the future reproductive 

 cells are distinguishable from those forming the body. Re- 

 searches since their time have shown the early origin of 



SPgMIATOSIlltSIS 

 i 



Speraato- 0^\ 



\ *\ SecondtPv ^^ 

 \' \ (ovum ana f ir :-t 



4tr 



(wJar bodyj 



And polar bcd:ts 



Mature ovua 



Jyjott.of^ f\ /\ full njjb.r of 

 ffcrtUijed I _ ^ I chrp%oaor:tos 

 ovu« with \ ^^ ^ / restored 



Fig. 6.— Diagram of gametogeiisis showing the par- 

 allel between maturation of the sperm cell and matur- 

 ation of the ovum (After Guyer.). 



germ-cells in leeches, threadworms, several insects, some 

 crustaceans and spiders. 



In the higher plants, however, soma plasm and germ 

 plasm reveal no visible difference although in some false- 

 graft hybrids Baur and Winkler found that one of the sub- 

 epidermal layers is probably alone responsible for the sex- 

 ual cells. 



The point to be emphasized in development is the 

 early setting apart of the primary germ cells before the 



44 



