s of the egg. The first division of the 
but the other quartettes are not followed. 
Fertilised Ovum 
rst quartette is shown, 
. 
Diagram showing the early cleavage 
The mesoblast and endoderm cells are labelled; all the cells which are derived from 
the first, second and third quartettes (labelled 1, 2 or 8 followed by a small letter) are 
members of the 
ectomeres. 
185 
2 4 8 16 
Cells. Cells. Cells. Cells. 
( lia 
ia 
| la? 
A a 
| | 2a 
1A 
| 9A 
AB 
1s 
i= 
| ( 152 
| i. 
| ( 20 
NB; 
( OB - 
We 
le 
| | ke 
(Gis 
| 2c 
lic! 
| 26 
CD + 
INE Tes dai, ldives5 7 
32 About 
Cells. 60 Cells. 
3a 
34 (4a Endoderm. 
“ (4A Hndoderm. 
3b 
ap (4b Endoderm. 
ob (4B Hndoderm. 
36 
30) (4c Hndoderm. 
(4C Endoderm. 
( 3d 
2D | 3p 
(4d Mesoblast. 
(4D Hndoderm. 
In Fia. 73 all the endo- 
69. 70, 71. 2B,2C,and derm cells except 4c 
2D, are not have again divided, 
seen in the and the mesoblast 
figure. 
cell has sunk into 
the segmentation 
cavity. 
