No. I.] THE EMBRYOLOGY OE LIMULUS. 43 



leave a space between it and the egg, and at the same time its 

 outline becomes regular and ellipsoidal. In half an hour the 

 granules begin to break up and become smaller, while the yolk 

 begins to swell, and at the end of an hour completely fills the 

 chorion. 



In four hours begin those strange modifications of the sur- 

 face already noticed by H. L. Osborn ('85) and by Brooks and 

 Bruce ('85). Viewed from the surface the eggs exhibit a num- 

 ber of fissures, usually at one pole of the ^^g, which strongly 

 simulate cleavage furrows (Figs. 4, 5, 6). I have not be enable 

 to kill such eggs quickly enough to preserve these furrows for 

 section. Even when dropped into hot water the surface would 

 become smooth before death ensued. 



Sections of such eggs present some features difficult of inter- 

 pretation. In the earlier phases near one pole there appears 

 a clear line inside the yolk, concentric with the surface, which 

 marks off a central from a superficial portion ; while in older 

 eggs (Fig. 7) the line has extended nearly around the egg. 

 Inside of this line were no features worthy of mention, and in 

 the several eggs sectioned no nucleus was to be found. Out- 

 side of the line the yolk becomes broken up into numbers 

 of columnar bodies — like the cells of columnar epithelium — 

 with rounded external ends. These yolk columns are separated 

 from each other by a slightly staining protoplasm (Fig. 8), 

 and the outer ends of these columns are more free from 

 yolk spherules than are the deeper portions. I think, notwith- 

 standing the apparent disparity of dates, that it was an 

 early stage of this process which Brooks and Bruce describe 

 when they say of an Q.gg of twenty-four hours " protoplasmic 

 processes or pseudopodia extend from the [protoplasmic] cap 

 into the yolk, and surrounding and including the substance of 

 the yolk divide this up into a number of yolk balls." After 

 a short time these motions of the external surface cease, and 

 the ^gg becomes as smooth as before, while in section no 

 change is recognizable except that there is a thin layer of 

 protoplasm — a true blastema ^ — over the whole yolk. 



^ As I have already indicated ('86, p. 1 16, foot-note), I use the term blastema 

 in the original sense. Patten defines ('84, p. 564) the blastema as "a thin nucle- 

 ated layer of protoplasm covering the whole outer surface of the yolk, and not 

 divided into distinct cells." He, however, suggests that it is not impossible that a 



