Embryonic History of the Germ-Cells of the Loggerhead Turtle. 317 



of such a fixative as faithfully preserved differential structural charac- 

 teristics. 



The material embraced in this investigation, selected from a large 

 stock supply, included embryos from the second to the thirty-second 

 day of incubation, distributed, preserved, and stained as follows: 



This material was collected on Loggerhead Key, Tortugas, Florida, 

 in the summer of 1914, while at the Laboratory of the Department of 

 Marine Biology of the Carnegie Institution of Washington. 



Three nests of eggs were available for the earlier parts of the series. 

 Two additional nests contributed to the later parts of the series. 

 The difficulties of removing the early blastoderm from the yolk were 

 not successfully overcome until the time had passed for preserving 

 stages younger than the end of the second day (5-somite stage). 

 However, this stage shows clearly the origin of the germ-cells from 

 among the yolk-sac entoderm, and the beginning of their segregation 

 into two bilateral cords near the lateral margin of the area pellucida in 

 the caudal half of the blastoderm; and it corresponds closely with von 

 Berenberg-Gossler's illustration (fig. 1) of his youngest lizard embryo 

 (5-somite stage). 



