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- 
Lepidosteus 
Fic. 6.— Diagrams showing the paths of migration in 4A, 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.) 
Arch = archenteron; Int. =intestine; Lat. Mes =lateral plate of 
mesoderm; Mes = mesentery; Meson = mesonephros; Myo = myo- 
tome; Noto = notochord; P. card = post cardinal vein; S.C = sex- 
cells; S.Gl=sex gland; Vit. 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- 
