48 BULLETIN: MUSEUM OF COMPARATIVE ZOÖLOGY. 
The cleavage of d™ occurs much later, and is likewise equatorial. 
I have not thought it necessary to introduce a special figure to show the 
cleavage of this minute cell. 
In d™ the cleavage also takes place late; it is meridional and equal. 
The resulting cells, de and de., are shown in Figure 72 (Plate 9). 
The minute dorsal cell de does not divide. 
D 
„718 D 
par 4 
" 
lan 30 | 29 
n * 
26 25 | 28 27 
26 23 28 +127 
22./| 24 18 a 
t i — 22 24 18 20 \ 
1 1 
* + b 
21 |23 17 Tan 23 17 [E] | 
R L L 
wi esie it al 4 as 18 WER 
jisi dá 2 | to 
| m $ 1 1 
ie Bt v9 E 
y V 
Dracram IV. DIAGRAM V. 
Quadrant D in the eighth genera- Diagram of quadrant A, B, or C, in 
tion, — except the dorsal cell, d7:16, the eighth generation. Only the second 
which does not divide farther. In exponent of the cells appears in the dia- 
the other cells only the second ex- gram, the first being 8. The small dor- 
ponent is expressed, the first being sal cell, (a, b, or c)7*10, does not divide, 
in all cases 8. The arrows connect remaining thus in the seventh genera- 
cells of common origin, and show the tion. The arrows connect cells of com- 
direction of the spindles at the pre- mon origin, and show the direction of 
ceding cleavage. the spindle at the preceding division. 
R signifies right; L, left; D, dorsal; R signifies right; L, left; D, dorsal; 
V, ventral. V, ventral. 
There are thus. 23 cells in the ectodermal part of the quadrant D at 
the end of the seventh cleavage. A diagram of this stage is annexed 
(Diagram IV.). Nearly this stage is represented in Figure 68. 
(2) The Quadrants A, B, and C. — Owing to the regularity in the 
size of the cells in these quadrants, and the fact that they are purely 
ectodermal, the conditions observed are fairly simple as compared with 
