CRANGON VULGARIS. iJ 



stages as well as in the distinctness of the cells from the 

 central yolk. 



After the present stage the changes in the arrangement 

 and character of the entodermal cells are comparatively 

 slight, exceptiiig an increase in number, nntil a much later 

 stage in the development. They remain scattered irregu- 

 larly through the yolk and bnt slovvly take a peripheral po- 

 sition. Atall stages nntil shortly before hatching they are 

 closer together in the neighborhood of the proctodeum than 

 elsewhere. With these remarks I will leave the further 

 description of the entoderm nntil it begins to form itself 

 into Organs, allowing the fignres to speak for themselves. 

 I have no actnal evidence as to migration among these cells 

 other than that afforded by sections. At the time of gas- 

 trulation (fig. 9) the yolk is free from nuclei while later 

 they are scattered throngh it, a fact which would seem to 

 necessitate migration from the point of origin. 



To anticipate a little, I may say I believe it is shown by 

 their future history, that these cells are truly entodermal 

 and that a "viteHophagons" career is not their sole function. 

 I have no reason to dispnte that they play an important 

 part in most arthropods in the metabolism of the yolk, and 

 hence they are so far viteHophagons. Such was stown to 

 be the case in Astacns by Reichenbach a decade ago. In 

 my paper on the development of Limulus ('85, p. 543) I 

 ascribed a similar function to corresponding cells in that 

 form and said that the lumen of the mid gut, and I might 

 have added, of its diverticula, arose from the actnal eating 

 of the yolk by these cells. Kowalevsky and Schulgin 

 ('86) attribute a similar function to cells occupying the 

 same position in the embryo scorpion, and Nusbaum, I 

 think, has adopted their views too completely in his de- 

 scriptions of Oniscus ('86) and Mysis ('87). These au- 

 thors, however, claim that vitellophagyis their §ole function, 



ESSEX INST. BULLETIN, VOL. XXI 1* 



