334 Papers from the Department of Marine Biology. 



the sex-cords, where as oogonia and spermogonia they undergo pro- 

 liferation and further differentiation. 



Considering all the forms studied, from Ascaris to man, the evidence 

 is all but complete for a morphologic continuity of the germ-cells, a 

 "Keimbahn," or germinal path. According to Buchner (1910) no evi- 

 dence appears for such a germinal path in annelids, mollusks, and echino- 

 derms, nor according to Fick (1906) for plants. But these are simply 

 instances regarding which our evidence is as yet very incomplete. 



The evidence derived from this study of the embryo of the loggerhead 

 turtle supports the theory of extra-regional origin of germ-cells and, 

 so far as it goes, the Keimbahn theory. The facts are most closely 

 in line with those reported by Allen for Chrysemyn, by Woods for the 

 dog-fish, and by Beard for the skate. 



This work had in view three chief objects: (1) to discover the origin 

 of the germ-cells and the route and manner of possible migration; 

 (2) a careful examination of the cellular contents of all blood-channels 

 with the expectation of removing a possible confusion between germ- 

 cells and certain blood-cells; (3) to find a basis for harmonizing the 

 results of von Berenberg-Gossler in the case of Lacerta with those 

 reported for other reptiles, and possibly other vertebrate forms. 



My first surprise was to find the facts in Caretta closely like those 

 described by Allen for Chrysemys. The germ-cells are segregated in 

 the entoderm from about the second to fifth day near the lateral border 

 of the area pellucida, from a point near the cephalic tip of the pro- 

 nephros to the caudal extremity. Up to the fourth day occasional cells 

 occur also in the area opaca near the border of the area pellucida. This 

 indicates the first step in the migration, namely, from area opaca to 

 lateral border of area pellucida caudally; since germ-cells disappear 

 later from the area opaca. In the area pellucida the germ-cells then 

 become fairly closely aggregated into two bilateral cords. These are, 

 however, not of uniform thickness throughout, but have an interrupted 

 or segmental character, suggesting "gonotomes." 



At about the fifth day germ-cells wander into the splanchnic meso- 

 derm and migrate medially. When the hind-gut becomes closed (from 

 the sixth to the tenth day) germ-cells become included in its mucosa 

 and in the more peripheral portion of wall. From here many migrate 

 through the mesentery across the angle of the crelom to the differen- 

 tiating sex-gland at the seventh day, a few apparently degenerating 

 within the gut-wall. At the thirty-second day they are distributed 

 among the peritoneal epithelium of the developing sex-gland and in 

 the subjacent mesenchyma. Only very occasionally is a cell found 

 extra-regionally at this stage, and apparently no sex-cords have as 

 yet begun to form; but neither is there the slightest evidence of a dif- 

 ferentiation of the so-called germinal epithelium into genital cells. 

 In the earlier stages a few germ-cells may be seen in mitosis and an 

 occasional cell may apparently divide at any stage. 



