JENNINGS: DEVELOPMENT OF ASPLANCHNA ITERRICKII. 99 
of the smaller cells of tho egg. The condition shown in his Figure 31 
he (91, p. 62) considers to be an exception, Later, he states that the 
polar cell becomes surrounded by small spherules, indicating that it is 
degenerating and falling to pieces. As showu in my Figures 51 and 
52 (Plate G), the vesicle d*? produced by the division of d'en in 
Asplanchna also becomes surrounded by large granules or spherules ; 
but these are not of the nature assumed by Zelinka; they are the result 
of a concentration of granules in the ventral cell dd, traceable from 
the eight-cell stage onward. In view of these facts, it seems possible 
that a similar division actually takes place in Callidina, and that the 
small cell lying between a and 6, in Zelinka’s Figure 31 is the small 
product of this cleavage, — the equivalent of d®? in Asplanchna. 
Tessin, in his study of Eosphora, also failed to follow the cleavage 
in detail to the 32-cell stage. He (86, p. 282) speaks of “ fortgesetzte 
Aequatorialtheilungen " of the cells in the three smaller quadrants ; his 
figures show the three quadrants composed each of a single row of six 
cells (Figs. 22 and 23). This corresponds to the condition in Asplanchna 
at a time when the dorsal cells (454—655) have divided equatorially, but 
when the remainder of these three quadrants are as yet undivided. 
Next, all the cells, except the large ventral cell d, are said to divide 
meridionally. It is probable, therefore, that the formation of the minute 
cell by the division of d** was overlooked, and that the cleavage is 
essentially as in Asplanehna. The cells of quadrant D are said to 
divide unequally at this cleavage, as is also the case in Asplanchna. 
The sixth and later cleavages of the ectoderm have not been studied 
in detail by other observers, so that a comparison of my results with 
observations on other forms is impossible. Diagrams of the sixth, 
seventh, and eighth elenvages for Asplanchna are given on pages 4 1, 46, 
48, and 53, that for the eighth cleavage being incomplete. 
The divisions of the entoderm cells have been followed somewhat further 
by Tessin and Zelinka, so that for these a comparison may be made. 
Nothing comparable to the unequal fifth and sixth cleavages of the 
entoderm cell (forming the small vesicles d and d.), shown in Fig- 
ures 38 (Plate 5) and 49 (Plate 6), have been reported by other 
observers. 
Later than these the cleavage of the entoderm in Eosphora (Tessin, 
'86) takes place as in Asplanchna (Figs. 64, 65, and 76-83, Plates 8-10) 
up to a stage comparable with that shown in Figures 77 and 78 (Plate 9), 
except that no cleavage of the smaller dorsal cell d? corresponding 
to the unequal division which I have shown in Figure 80 (Plate 10) was 
