368 EDWIN G. CONKLIN 



Because of this framework the stratification of egg substances 

 in centrifuged eggs is never complete, but strands of spongioplasm 

 prevent the free movement and stratification of substances 

 according to their relative weights (pp. 329, 333). 



3. The spongioplasm is highly elastic and contractile and when 

 it is stretched or distorted it tends to come back to its normal 

 form and to bring back to their normal positions displaced con- 

 stituents of the cell (pp. 369, 373). 



4. Mitotic figures, especially after the metaphase, are more 

 firmly bound to the peripheral layer than are resting nuclei and 

 centrospheres ; the latter are always firmly united and the cen- 

 trospheres are connected to the peripheral layer of the cell at 

 the point nearest to the animal pole (pp. 333-335, 351-353). 



5. As a result of these connections mitotic figures as a whole 

 can be displaced only before the metaphase ; after that stage they 

 may be stretched or distorted but their astral radiations can 

 rarely be separated from the peripheral layer (pp. 336, 337, 

 349). 



6. Centrospheres and nuclei of resting stages may be displaced 

 in any direction, but because of their connections with each 

 other and with the periphery they always maintain a definite 

 axial relation, the centrospheres lying between the nuclei and 

 that portion of the periphery which is nearest the animal pole. 

 Nucleus, centrosphere, mitotic figure — each has a polarity of its 

 own, but all are held together in a definite relation to the cell 

 body by the spongioplasm (pp. 352, 362, 363). 



7. The persistence of the original polarity in centrifuged eggs 

 in which most of the parts have been displaced and the return of 

 those parts to their normal positions is due to these connections 

 of spongioplasm, which are elastic and contractile (pp. 358, 374). 



8. There is no good evidence that the polarity of a cell is a 

 resultant of the electric charges carried on colloidal particles or 

 on cell membranes. When eggs are caused to fuse together 

 each component preserves its own polarity (pp. 366, 368). 



9. Neither external nor internal surface tension phenomena are 

 able to explain satisfactorily the persistence of cell polarity in 

 centrifuged eggs (pp. 367, 368). 



