8 THE DEVELOPMENT OF 



regularly scattered through the yolk but still remain closer 

 together near the region of their origin. Each nucleus is 

 deeply and nearly evenly stained, the chromatin reticulum 

 showing less plainly than in the mesoderm or ectoderm 

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

 stages. 1 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 corresponding to these nuclei, as is the case in Lim- 

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

 plasm surrounding it apparently form the entire cell, the 

 yolk being something external and intercellular. Reinhard 

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

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

 derm by 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 filled with yolk or. the secondary yolk 

 pyramids, described and figured by both 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 irregular manner, and the nuclei so far as I 

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

 gon, as has been said before, is more like Palsemon than 

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

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

 larity with which the entodermal nuclei are arranged in all 



1 It hardly needs to be said that in order to more clearly distinguish 

 between the different germinal layers beyond that afforded by the 

 colors, I have adopted a conventional method of representing the com- 

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

 drawings, however, I have endeavored to represent the exact histolog- 

 ical appearance so far as the reproductive process would allow. 



