No2z:) J77CRODEUTOPUS GRYLLOTALPA COSTA. 307 
dividing the egg into two equal parts. The two blastomeres 
then flatten against each other, and the living egg presents 
the same form as it did before cleavage. I have never seen 
the blastomeres unequal in size at this stage, as Van Beneden 
and Bessels and Della Valle describe for the gammarids. 
4-cell stage. — One hour elapses before the completion of the 
second division. Fig. 19 represents an optical section of an egg 
which was killed half an hour after the first division. The proto- 
plasm has almost divided and the second cleavage furrow has 
begun to appear. This cleavage plane makes an acute angle 
with the first plane, giving rise to two small and two large blasto- 
meres, the smaller blastomeres being even less than one-half the 
size of the larger ones, as shown in Fig. 1. When the egg comes 
to rest the two large cells flatten against each other, pushing 
the smaller ones apart in such a way that one lies above and 
the other below the plane of the equator, this plane being sup- 
posed to pass through the long axis of the egg and at right angles 
to the first and second cleavage plane; z.¢., in Fig. 1 it lies in 
the plane of the paper. No rotation of the blastomeres, as 
described by Wagner for Melita ('91), has ever been observed; 
the blastomeres always flatten against one another without 
changing their position. I always find, at this stage, two cells 
smaller than the other two, and not three of the same size and 
one somewhat smaller, as in the gammarids described by Van 
Beneden and Bessels ('69) and Della Valle ('93). Sometimes 
one of the two smaller blastomeres is larger than the other 
small one, but never as large as the large ones. 
For convenience in describing the later stages, I shall name 
the larger cells AS and CD, the small cell above the equator 
EF, and the remaining one GAH. 
S-cell stage. — At the end of the fifth hour an equatorial 
furrow divides the egg into four micromeres and four macro- 
meres (Fig. 2). The four micromeres bear to each other the 
same relation in size as the four macromeres, and the larger 
micromeres are smaller than the smaller macromeres. When 
the egg comes to rest the two large macromeres flatten against 
each other, and likewise the two large micromeres, while the 
two small macromeres and the two small micromeres are forced 
