8 THE DEVELOPMENT OF 



regularly scattered through the yolk but still remain closer 

 together noar tlie region of their origin. Eacli nucleus is 

 deeply and iicarly evenly staiiied,tlio chromatin reticnlum 

 showing less plainly tlian in the mesoderm or ectoderm 

 cells, a peculiarity which, however, is lost in the hiter 

 stages.^ Each nucleus is surrounded by a thin layer of 

 slightly staining protoplasm which sends off delicate pseu- 

 dopodal processes between the masses of the yolk. I have 

 never been able to see that the yolk was divided into 

 masses correspondingto these nuclei, as is the case in Lim- 

 ulus (seif, '85) but in Crangon each nucleus and the proto- 

 plasm surrounding it apparently form the entire cell, the 

 yolk being something external and intercelhüar. Reinhard 

 ('87) came to the same conclusion with regard to the ento- 

 derm cells in Porcellio. After the ürst formation of the ento- 

 dermby invagination, the resulting cells in Crangon lose 

 their continuity and not until a comparatively late stage, 

 do they again attain the condition of a layer. The large 

 entoderm cells fiUed with yolk or the secondary yolk 

 pyramids, described and figured by l)oth Bobretzky and 

 Reichenbach in Astacus, do not exist in Crangon. The yolk, 

 it is true, is divided into masses or spheres of varying size 

 but in a very irregulär manner, and the nuclei so far as I 

 have been able to discover bear no relation to these. Cran- 

 <^on, as has been said before, is more like Pak^mon than 

 like Astacus inits lacking a lumen to the mid-gut, but it dif- 

 fers from Bobretzky's figures of Palaemon in the irregu- 

 larity with which the entodermal nuclei are arranged in all 



1 It hardly iieeds to be said that in order to more cleaiiy distinguish 

 between tlie different germinal layers beyond tliat afforded by the 

 colors, I have adopted a conventional method of representingthe com- 

 ponent cells and nuclei in the general ligures. In the more detailed 

 drawings, however, I have endeavored to represent theexact histolog- 

 ical appearance so far as the reproductive process would allow. 



