80 Animal Morphology. 



as it exists in the animal kingdom, no outline would 

 be attempted in such an intricate subject. But such as 

 it is, in its leading outlines, is here briefly laid before the 

 reader. 



A general assumption is made that all cells are more or 

 less formed of an inner and outer wall, here technically 

 called membrane ; and membrane in its lowest form is called 

 cell membrane. This does not imply that the inner wall 

 may not be continuous with and constitute a part of the 

 soft or granular part within the cell, but in vegetables all 

 cells and morphologies consist of binary membrane. 



On the other hand, it is assumed that all cells of an animal 

 origin have within them, or by differentiation have pertain- 

 ing to them, the essential conditions of an inner, middle, 

 and outer membrane, one of which is called contractile 

 membrane. 



In animals a plus membrane is added, or a plus material 

 property is added to that pertaining to vegetables namely, 

 a contractile membrane. 



The grand distinction, therefore, in cell morphology and 

 differentiation, between animals and vegetables, is, that in 

 material organism, vegetable membrane is essentially a 

 bipartite membrane, and animal membrane is an essentially 

 tripartite membrane. 



What will best illustrate the nature of a tripartite mem- 

 brane is the simple silicious porifera or sponges. 



Granting the outer wall to be a more or less silicious 

 deposit in the jelly-like substance of the sponge, and the 

 inner contained sarcode, or jelly, to be the inner coat ; yet by 

 imbibition from without, as by capillary attraction, fluid is 

 constantly and imperceptibly flowing from without inwards ; 

 but all through the pores and half tubular structure of the 

 sponge, fluid may be seen thrown off at repeated intervals, 

 from these open spaces filled with sarcode. 



