302 DR THOMAS H. BRYCE ON 
up, on the other hand, the balloon is divided into two (fig. 2). This simple model is 
not required, of course, to prove that such a system of threads, if contractile, or under 
elastic tension, and attached to a cell membrane at the equator, will produce, or at any 
rate initiate, cell division. HEIDENHAIN’s or RHUMBLER’s models show this quite well, 
but the device described imitates in this one respect, I think, even better what I 
believe actually occurs in this special case. 
There is no apparent sign of growth of the cell membrane at the equator, which 
is one of RHUMBLER’s secondary factors. When once the furrow is produced it quickly 
completes itself, because the external pressure is now related to the two centres, and 
division takes place in the neutral zone between them. That the subequatorial threads 
TG ay le Ihidek, 2% 
become stretched out in the axial line between the centres is seen in the photograph 
Pl. V. fig. 40, which closely resembles text, fig. 2 representing the model. 
That the protoplasm has considerable ductility seems to be indicated by the tardy 
return to the reticular or alveolar condition, and also by the drawing out of the spindle 
remnant between the daughter cells into a thread of some length. 
Turning for a moment to alternative hypotheses as to the structure of the corpuscles, 
I think the idea that the phenomena are to be attributed to lines of strain in a homo- 
geneous and continuous colloid substance may be put aside. Although the alveolar 
theory of BirscH.i is excluded in the strict sense of the term by the size of the alveoli, 
the protoplasmic framework behaves much as the hyaloplasmic framework does im 
RHUMBLER’S theory and the elastic framework in his model. 
