FATE OF BLASTOPORE ETC. IX CHELONIA IQß 



the oTowing edge (Ümwüclisuug.^nind), in the manner of Hertwig, is 

 not defensible. Of this I sliall speak anon. 



Diagram V, the first of the Clielonian series, is someAvhat like I, 

 but is in reality very different. In tlie first place, the large yolk- 

 mass (Yni. 2) exposed below the limits a-a of the blastoderm in V is 

 not the same as the large yolk-mass (Yw. 1) in I, although s(j much 

 like it ill appearance. That mass in I' is the sccondarti yolk-mass. The 

 primary yolk-mass or the mass correspondiiig to that of tlie Elasmo- 

 brancliii is represented in a surface view by the small shaded area, 

 (F;//. i) behind the line, 1-1, in the posterior part of the embryonic 

 region. The crescentic line, 1-1, represents the anterior lip of the 

 blastopore and corresponds to the ])Osterior part of the blastoderm edge, 

 1-1, in I. 



In VI, the blastoderm has grown to the edge h-h. The embryo 

 has grown in length from the line 1-1 to the Une 2-2, which 

 represents the anterior lip of the lilastopore noic become straight across. 

 As I have said before (/). 7S), I leave for the present the question 

 open whether the embryo has grown in length by concrescence or by 

 intussusception. The shaded area (T;;/. 1) behind the line 2-2 

 represents as before the primarii yolk-mass. 



In A'll, the blastoderm has covered the secondary y(_)lk-mass to 

 the line c-c. In the embryonic region, the blastopore li[)s 4—1 have 

 become horse-shoe shaped. The remnant of the primary yolk-mass 

 (Ym. 1) is enclosed within the horse-shoe. The lines 1, 2, corres))ond 

 to the lines similarly marked in III, and the lines o, 4, show further 

 growth. 



In \'III, the secondary yolk-mass is covered by the blastoderm 

 to the line d-tJ. There has taken place a great change in the blasto- 

 pore. 'Jlie fi^remost part of it has become the dorsal opening 



