JENNINGS : DEVELOPMENT OF ASPLANCHNA HERRIGKII. 71 



or the lesser axis of the cells, so that fx'om these cases uo evidence ou 

 our question can be gained. But in later stages the crowding together 

 of the cells results in greater or less alteration of the cell axes in rela- 

 tion to the axes of the egg. In Figure 68 (Plate 8), for example, the 

 long axis of the cell d^'^^ is not parallel with that of d^-^'^- the two are 

 wedged apart dorsally by the cell o?^-", so that neither one points 

 exactly to the animal pole of the egg. The two spindles are likewise at 

 an angle with each other, and lie in the long axes of the cells, instead of 

 exactly dorso-ventral. The same is true of the cells c''-' and c''^^ in the 

 same figure. Again, in Figure 74 (Plate 9) the spindles of d^-'^'' and 

 d^'^^, though in general direction dorso-ventral, form an angle with each 

 other, the one in d^-^'' being modified in position so as to lie in the 

 longer axis of the cell, while the one in d^'^^ lies in the shorter axis of 

 the cell. In the entoderm the same thing is strikingly true of the 

 spindles shown in Plate 9, Fig. 79, and Plate 10, Fig. 83, for there the 

 spindles form various angles with one another, all lying in the longer 

 axes of the cells. 



But these cases do not necessarily lead to the view that the form of 

 the cell modifies even slightly the position of the spindle. It is 

 possible that in each cell the axis of the spindle is determined other- 

 wise, so that alteration of the position (not form) of the cell necessarily 

 produces an alteration in the direction of the spindle. Thus in Figure 

 68 (Plate 8), if the cells c?^-" and d'^-^'^ are ellipsoids of fixed form in 

 which the two ends of the spindles have predetermined positions, in case 

 the cells are forced apart, as in this instance by d^^'^'', the ends of the 

 spindles will be forced apart to the same degree. Though we know that 

 the cells are not ellipsoids "of fixed form," yet we also know that the 

 form of the cell is greatly injiaenced by the direction of the contained 

 spindle. It is possible that the cytoplasm of the cell tends to group 

 itself symmetrically about the contained spindle, so that the direction 

 of the spindle is the primary fixctor, the fiict that it lies symmetrically 

 in one of the axes of the cytoplasmic mass being a secondary result. 

 This becomes very probable when we examine from this standpoint the 

 change of form of the very irregular cell d^-^, shown in Plate 5, Fig. 

 37 (surface view), and Fig. 38 (section), before the formation of the 

 spindle, and in Plate 7, Fig. 54 (surface), and Plate 6, Fig. 48 (section), 

 after the formation of the spindle. In this cell, before the forma- 

 tion of the spindle, the shape is so irregular that it is not possible 

 to distinguish a definite ''short axis," and no plane would divide the cell 

 into symmetrical halves. But as the spindle is formed, the cytoplasm 



