388 RICHARD EVANS. 



number of cells that can take part in the formation of a group 

 cannot pass a certain limit. Consequently, as the individual 

 elements of the cell groups multiply by division, it seems a 

 well-founded conclusion that the groups themselves multiply 

 in the same way.^ 



The large number of cells found in the bigger groups might 

 be accounted for on the supposition that the individual cells 

 have divided since their liberation from the groups of type B. 

 Though this supposition may be to some extent true, it is 

 more probable that the difference in the number of cells which 

 constitutes a cell group or a flagellated chamber in type C 

 corresponds to a similar diff'erence in the number of nuclei in 

 the multinucleated cytoplasmic masses of type B. 



The cytoplasm of the individual elements of the cell groups 

 is usually clear, but may contain a few granules which are 

 either reduced yolk granules or bodies of the same nature as 

 the refringent granules already described as existing in the 

 flagellated cells, and also in all the cells of the inner mass. 

 Another very remarkable fact is that they occasionally contain 

 a small nutritive vacuole, a fact which points to their origin 

 from the cells with vesicular nuclei. 



Another feature of some of the cell groups in this type is 

 that their individual cells develop collars and flagella in all 

 respects like those of the collar-cells in the adult sponge. It 

 is true that the greater number of these groups consist of 

 cells which have not as yet developed these organs; and it may 

 be further stated that unless great care is taken in the pre- 

 servation of the larvge, all of them, without exception, will be 

 without collars, and will present only a kind of process possess- 

 ing a more or less conical shape, and pointing towards the 

 cavity inside the group of cells. The collars unite by their 

 margin to form the so-called " membrane of Sollas " (figs. 7 

 and 7 a). 



These cells, which from this stage onwards may be called 

 collar-cells, present the same general arrangement and the 



1 For further remarks on ilie nmltiplicaiiou of the coUar-cplls and of the 

 flagellated chambers of. Appendix D. 



