CASTLE: EMBRYOLOGY OF OIONA INTESTINALIS. 204 
nearer to tho superficial than to the deep ends of the cells. The most 
anterior mesenchyme cells appear in Figure 77 (A, ASN, Be, BS), 
They are descended from 45, 579 (Plate X. Fig. 62), in which cells the 
division leading to the eighth generation occurred at a stage considerably 
earlier than this. (See Plate X. Fig. 67.) Im this caso also (A1, B2) 
the spindles stood vertically and division was unequal, but the more 
superficial daughter coll was the larger, the deeper one being small and 
almost entirely filled with unassimilated yolk. (Sce Plato: XRF T 
ARA e 13592; Bene) 
The posterior chorda cells (47, Fig. 77, and el in the left half of 
Fig. 76, not lettered) show no essential change since the last stage figured 
(cf. Plato X. Figs. 66 and 67). The anterior chorda cells do not appear 
in the sections figured ; they are still iu the seventh generation. 
Division has been completed in 0%, D**, 08% 0% (Fig. 12), four of 
the neuro-museular cells lying at the margin of the blastopore. (See 
Figs. 74-76, D8, 9, 7935 7949 and the corresponding cells in 
quadrant C) ‘The other cells of the neuro-muscular ring and the entire 
ectodermal group have not been essentially modified since the last stage 
figured (Fig. 72) 
If the foregoing account is correct, the embryo, sections of which are 
shown in Figures 73-77, contains one hundred and twenty-eight cells, 
distributed as follows. 
Ventral hemisphere : — 
Fctodermal group : 
S | 
( ectoderm. 
61 cells in the 9th generation 
| nervo cells. 
Equatorial band : 
2 ectoderm cells im the 9th generation. 
8 neuroanuseular cells in tho 9th generation. 
10 [2 “ce 13 "th [13 
2 [23 [17 [11 Tth [11 
8 mesenchyme de sth d 
2 mesenchyme ds Tth My 
229 : 
96 
Dorsal hemisphere : — 
2 mesenchyme cells im the 7th generation. 
10 chorda i "9 fc 
&« [1 [11 
20 endoderin 
