644 JOHN BEARD, 



the nose is a rather wide pit, and the auditor}^ organ is a simple 

 vesicle. The upper jaws have not yet begun to form. The develop- 

 ment of mesoblastic somites has almost or quite ceased, and their 

 number varies from 144 to 150. The latter number seems to be 

 the final limit. The neureoteric canal is either just closed or closing. 



The two embryos to be described are R. hatis No. 441 (21 mm) 

 and No. 453 (22 ram). It is possible, that they were sister-embryos, 

 for both the eggs were obtained on March 25th, but embryo No. 441 

 was killed on July 15th, embryo No. 453 on July 30th. As will be 

 seen, the two embryos are very much alike in the number and distri- 

 bution of their germ-cells. 



In jR. hatis No. 441 the first normal germ-cell is met with in the 

 pronephric region, a find recorded by Rabl. Then for about 80 

 sections there are no others, with the exception of 2 in abnormal 

 situations. Then a single one is again met with, and after some 25 

 sections there are 4 others. From this point for some distance 

 caudalwards they are met with in greater numbers and in practically 

 every section. In the following 7 rows of sections, containing from 

 25 to 30 sections in each row, there are from 15 to 25 normally 

 placed germ-cells in each row. Then they rapidly decrease in 

 number, and in the hinder part of the abdomen there are very few. 

 In the last 4 rows (embracing about 150 sections) there are only 25 

 germ-cells all told. 



The total number of normally placed germ-cells of this embryo 

 is very small, being only 126. Other 18 were counted as situated on 

 the mesentery, i. e., in the splanchnopleure ventrad of the germinal 

 nidus; 8 were within the mesentery, and 9 were found in other places. 

 The total is 161. 



Of the vagrant germ-cells 2 were applied to the germinal nidus 

 without being in any sense within it, 2 were on the subintestinal 

 vein, 2 were in the somatopleure, 1 was free in the cloacal cavity, 

 1 was in degeneration, and the remaining one was a germ-cell on the 

 splanchnopleure of the yolk-stalk outside the body of the embryo and 

 just beneath the vitelline vein. 



Near the germ-cell just spoken of, and 2 sections further for- 

 ward there was a "concentric corpuscle" on the opposite side, lying 

 in the splanchnopleure close to the subintestinal. This may be inter- 

 preted as a degenerate germ-cell There was also another such 

 corpuscle in the aorta at the extreme end of the abdomen. These 2 



