No. 2.] EMBRYOLOGY OF THE AMERICAN LOBSTER. 229 



gathers between them. I have observed much the same in 

 Libiiiia. In Crangon a vitelline membrane is not present. 



Rathke ('36) claimed that the egg of Astacus had a "vitelline 

 membrane " separated from the " chorion " by a fluid, and Dohrn 

 claimed the same for the egg of Palinurus. Mayer (jj) has 

 called attention to the fact, however, that both Rathke and Dohrn 

 may have been considering a " Blastodermhaut," which latter 

 certainly does occur in Homarus, but at a little later stage. 



Cleavage Stages. 



Sections were made through eggs similar to those just de- 

 scribed. They show that up to the so-called "eight-cell stage" 

 the nuclei exert no apparent influence on the external portion 

 of the yolk-ladened egg, there being no early cleavage stages, 

 so far as the entire egg is concerned. 



The earliest stage which I have found represents an egg 

 with two nuclei. Fortunately the knife passed through both of 

 these, as shown on PI. XIX, Fig. 2. 



The nuclei, as would be expected, are individually very much 

 smaller than was the mature primordial vesicle and relatively 

 minute when compared with the egg of Crangon, Kingsley (Sy). 

 Each is surrounded by a clearly radiate mass of protoplasm, the 

 rays extruding out between the yolk masses. Oil vacuoles are 

 abundantly found, except in the immediate neighborhood of the 

 nuclei, where the investing protoplasm is quite homogeneous. 

 The peripheral portion of the egg is still granular, as was the 

 later ovarian egg, the yolk spheres being more closely juxta- 

 posited as the centre of the egg is approached. Though a deli- 

 cate layer of protoplasm invests the egg, no distinct membrane, 

 other than the " capsule," can be demonstrated. The plasma 

 cells are still represented by chromatin grains, extremely mi- 

 nute, which are abundantly found in favorable preparations scat- 

 tered in the interstices between the yolk spheres. They are no 

 longer confined to the periphery, however, but have advanced 

 towards the centre and formed an indefinite ring, as figured 

 on PI. XIX, Fig. 2. The ring marks the dividing line between 

 the peripheral granular yolk and the central less granular 

 portion. 



Sections made through eggs of the next following day show 



