CHAPTER XVI. 



THE SHAPES OF ANIMAL CELLS. 



§ 260. Among animals as among plants, the laws of mor- 

 phological differentiation must be conformed to by the mor- 

 phological units, as well as by the larger parts and the wholes 

 formed of them. It remains here to point out that the con- 

 formity is traceable where the conditions are simple. 



In the shapes assumed by those rapidly-multiplying cells 

 out of which each animal is developed, there is a conspicuous 

 ^^^ subordination to the surrounding actions. 



Fig. 294 represents the cellular embryonic 

 mass that arises by repeated spontaneous 

 fissions. In it we see how the cells, origin- 

 ally spherical, are changed by pressure 

 against one another and against the limit- 

 ing membrane ; and how their likenesses 

 and unlikenesses are determined by the likenesses and un- 

 likenesses of the forces to which they are exposed. This fact 

 may be thought scarcely worth pointing out. But it is 

 worth pointing out, because what is here so obvious a con- 

 sequence of mechanical actions, is in other cases a conse- 

 quence of actions composite in their kinds and involved in 

 their distribution. Just as the equalities and in<=^qualities of 

 dimensions among aggregated cells, are here caused by the 

 equalities and inequalities among their mutual pressures in 

 flifferent directions ; so, thcujrh less manifestly, the equalities 



