CRANGON VULGARIS. 125 



karyoldnetic figures were visible in the yoiing stages, even 

 where cell division was actively going on. 



Witlaczil, in bis masterly paper on the clevelopment of 

 the Aphides ('84), agrees with the others that the nucle- 

 ated yolk spheres represent the endoderm and that they 

 later give rise to the "Wanderzellen," of whose wander- 

 ing, however, he has doubts. These yolk spheres he re- 

 gards as prodacts of segmentation, but he makes no 

 comments upon their relatious to the blastopore or to any 

 invagination. 



Korotneff ('85) , studying Gryllotalpa, arrives at conclu- 

 sioiis much like those of Patten. The yolk cells all mi- 

 grate to the surface and there take part in the formation 

 of the smooth blastoderm. Here some of the blastoder- 

 mic cells (usually in the neighborhood of the scarcely ap- 

 parent primitive streak) become larger than their fellows 

 and send protoplasmic prolongations down into the yolk, 

 and then sink themselves into that substance. This takes 

 place by scattered cells here and there and forms what this 

 author terms " diffuse gastrulation." He makes no men- 

 tion of mesodermal cells sinking into the yolk, but de- 

 rives his entoderm solely from these amceboid cells arising 

 from the blastoderm. This constitutes oue of the differ- 

 ences between him and Patten ; another consists in the 

 fact that Patten has the 3^olk cells budded from those of 

 the blastoderm, while Korotneff has the blastodermic cells 

 themselves sink into the yolk. 



Bruce has a different view. In Thyridopteryx ('85) 

 the germinal area becomes two cells deep, apparently by 

 a delamination which takes place beneath and at the sides 

 of the primitive groove. The inner layer then separates 

 from the other and, Splitting into twobands, grows laterally 

 and dorsally, and portions of it then extend around and 

 enclose the yolk. These are said to "form the epithelium 



