94 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
“pass into the yolk hemisphere, where it transforms yolk material into 
protoplasm ; the second merocyte, formed partly in this way and partly 
from previously existing protoplasm, issues as the second blastomere, 
while the first becomes simultaneously cut off from the yolk ... the 
nucleus of the third merocyte is derived from that of the second; the 
latter becomes spindle-shaped, and gives off a nucleus, which, accom- 
panied by little or by no appreciable quantity of protoplasm, passes into 
the yolk. . . . The third merocyte, in similar manner, while emerging 
as a blastomere, divides and gives off a nucleus to the yolk, which in a 
similar manner gives rise to new merocytes and blastomeres.” 
It is evident, as indeed Groom distinctly states in another place, that 
he regards the yolk as non-nucleated and receiving nuclei from the suc- 
cessively formed blastomeres. In the discussion of the first cleavage I 
have pointed out that a nucleus from “the first blastomere” (the cell 
ab? in this paper) does not pass into the yolk-cell just before the separa- 
tion of the two cells. This also applies to all succeeding cleavages. The 
yolk-cell does not derive its nucleus from successively formed “ proto- 
plasmic” cells (‘ blastomeres”) — such a description is inaccurate and 
misleading. In no case can either “blastomere”’ or the yolk-cell be 
said to derive its nucleus from the other, for the micromeres are merely 
the result of ordinary unequal division, which differs from the division 
of cell ab? in the inequality of the produetss but not in the method by 
which it is brought about. 
The term “‘ merocyte” conveys the idea that the protoplasm is more 
or less sharply distinct from the yolk, as in the case of eggs which un- 
dergo superficial cleavage. This is evidently the idea intended to be 
expressed in the above quotations from Groom. Neither living eggs 
nor stained sections support such an interpretation. A considerable 
part of the yolk-cell cd? is protoplasmic, the yolk and protoplasm being 
so mingled that there is no justification for the use of the term “ mero- 
cyte.” I cannot agree with Groom’s statement that throughout the 
main portion of its mass the yolk-cell contains little protoplasm. Pro- 
toplasmic processes extend even among the oil droplets which lie near 
the periphery at the vegetative pole of the egg (Fig. 27). I cannot 
confirm the statement (p. 198) that there is little protoplasm left in 
the yolk-cell immediately after the separation of a new blastomere, and 
that the nucleus rapidly transforms yolk into protoplasm to form the 
new blastomere. The amount of yolk is not very much diminished 
before the sixth cleavage. This is in accord with the facts known 
in the case of the development of other animals, for rapid transforma- 
