32 



GERM-CELL CYCLE IN ANIMALS 



of origin and the germinal ridge is too great to be 

 traversed in any other way. 



Professor B. M. Allen, who has made extensive 

 studies of the germ cells of many species of verte- 



LepMosteus 



LepldosUus 



Fig. 6. — Diagrams showing the paths of migration in A, a turtle, 

 Chrysemys marginata ; B, a frog, Rana pipiens ; C, a fish, Lepidos- 

 teus osseus, and D, the dog-fish, Amia calva. (From Allen, 1911.) 

 Arc/i = archenteron; /n^ = intestine; La^ Mes = lateral plate of 

 mesoderm; Mes = mesentery; Meson = mesonephros; M2/0 = myo- 

 tome; A^oto = notochord; P. card = post cardinal vein; S. C = sex- 

 cells; S.Gl = sex gland; V it. End = vitelline endoderm; W.D = 

 Wolffian duct. 



brates, makes the following statement regarding this 

 phase of the germ-cell cycle : 



"The sex-cells are migratory to a high degree. 

 The path and time of their migration may vary 

 greatly within a given group of animals, as illus- 



