254 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
It was predicted from the position of the spindle in this ecll that the 
division would be unequal, the more centrally and dorsally situated 
daughter cell being the smaller. This smaller cell is represented by c*?* 
(Fig. 82), but only the upper end of its large sister cell, cè, appears in 
this section. In Figure 83 (Plate XI.) we see the deeper portion of c9, 
which contains a nearly horizontal spindlo. 
Posterior to the pair of cells just described are the descendants of C7 
(Fig. 71), the next to the hindmost of the mesenchyme cells in the left 
half of the embryo. In Figure 74 they were in the eighth generation 
(088, 915), One, the smaller, still remains in that generation (0%, 
Fig. 82), but its larger, more deeply situated sister cell has passed into 
the ninth generation, and is now represented by C99?» O°, Figure 82. 
The direct evidence of mitosis has not been observed for the division 
hero assumed, but very strong indirect evidence for it exists in the fact 
that at the last cell division in the mesenchyme cells, C78 divided earlier 
than ce? (cf. Figs. 74 and 75). Ifthe same order of division is followed 
in case of the daughter cells, division ought to occur earlier in 0%% than 
3, But the latter cell is scen in Figure 83 to be in process of 
g 
in c! 
division ; therefore it is reasonable to suppose that at the same stage the 
former cell has already divided. 
The small posterior mesenchyme cells, C75, Di, lie one behind the 
the other deep down in the floor of the gastrula (Fig. 83), just posterior 
to the endoderm cells and overlaid by muscle cells, — for such the in- 
vaginated cells of the neuro-muscular ring become. 
eim 
These musel 
: cells have been erowded inward and downward at the 
consequence of the rapid contrac- 
posterior margin of the blastopore in 
tion of that opening. 
[n the most posterior pair of muscle cells, viz. 07%, D 7 
‘OSI \ ob to oeeur, as alread tated, at ta earlier tha 
N 7 wıchter cel ising from that division ( dily recog 
7 : 4 1 00) Th nuci i uid 
1 1 yet el ho 1 1 415 
n t tal 
th 1 le ec t ( ot ) f npt 
n ou l A T ( m 
hed from tl ( m on ) 1 ian fron 
mesenchyme cells on the other. by their large cir considerable 
size, and the peculi ır stain ibility of their ] They resemble 
very closely in stainability the nervo colls ly to the blasto 
