I20 MAY M. JARVIS. 



Wheeler's (1899) work on the lamprey is conclusive evidence ; he 

 found the germ-cells first in the entoblast lateral to the myotome, 

 in the mesoblast after it is cut off, and then moving into the 

 median line. Bouin (1900) argues that the germ-cells arise 

 directly from the peritoneal and sclerotome cells of the germinal 

 region, but admits that they may also come from the yolk-sac. 

 Nussbaum (1901) records their migration in Gallus from the 

 splanchnic mesoblast, where they appear as large, yolk-laden 

 cells, the ova being their descendants. Woods (1902) gives an 

 interesting account of the germ-cells in Acantldas, where they 

 first appear in the entoblast or in the yolk, migrating to the 

 germ-gland anlagen. 



Beard (1902) studied the germ-cells in various selachians. In 

 Raja he traced them back to late cleavage stages ; many come to 

 lie in the germinal cavity, whence they migrate into the embryo, 

 and along the space between entoblast and mesoblast to the ger- 

 minal nidus ; some leave this normal path and reach other organs 

 of the embryo. He considers that some of these latter degenerate. 



Bohi (1904) found that the first germ-cells appear in the trout- 

 embryo not before the twenty- fifth day after fertilization ; in the 

 salmon, not before the thirty-first. They lie in the splanchnic 

 and somatic mesoblast, being pushed into the somatic by the 

 growth of the splanchnic. 



Allen (1906) working on CJiryscviys, found that the germ-cells 

 originate in the entoblast at the edge of the area pellucida, in a 

 zone extending from a point opposite the anterior end of the 

 pronephros to a point behind the embryo. They migrate in the 

 entoblast to a point beneath the notochord, and upward through 

 the sclerotome to the germ-gland anlagen. A part of these also 

 "lose the way." In Rana pipicns (1907) he finds that they 

 develop from a group of apparently indifferent entoblast cells in 

 the dorso-median region ; this group is cut off from the other 

 entoblast cells by the growth of the mesentery, or more probably, 

 moves above the mesentery ; later, the cells migrate laterally 

 coming to lie in the paired germ-gland anlagen. 



Through the courtesy of Dr. Allen, I have been enabled to 

 examine the more important stages in the migration of the germ- 

 cells of Cliryseniys ; they are similar to my own material, as my 



