496 THE ANIMAL CELL. 



cell divides into portions which are sensibly equal, in this into unequal 

 parts. 



Cells are said to arise from endogenous generation when they make 

 their first appearance in the cavity of a former cell, of which 



Endogenous Jrir . *. . . 



generation of the endochrome exhibits a disposition to divide into many 

 small portions, at first doubtfully, then more distinctly, and 

 each one of these portions obtaining a covering investiture or primordial 

 utricle for itself. The process continues until the young brood of cells 

 has reached a certain degree of perfection, when they -escape from their 

 confinement, either by the fissuring or deliquescence of the old cell wall. 

 The young cells may now lead an independent life and grow rapidly. 

 In this manner zoospores arise, which are young cells having for a time 

 a power of locomotion, from cilia which have been developed from their 

 walls, or for other reasons. 



The reproduction of cells l>y endogenous generation is commonly at- 

 tributed to an action arising in the endochrome which brings on its sub- 

 division into portions. From the fact that these portions are eventually 

 found clothed with a primordial utricle, we might be led to suspect that 

 the original seat of the action is in this, as in the preceding cases, that 

 portion of the original cell which, undergoing projection internally, di- 

 vides the endochrome and incloses the portions in its meshes. Such 

 membranous projections may be difficult of detection in the first instance, 

 because of their extreme tenuity ; nor is the fact that the zoospores 

 move freely in the cavity of the mother cell just before their escape at 

 all in contradiction to this. 



THE ANIMAL CELL presents a structural arrangement diifering from 

 Peculiarity of the vegetable in this, that it does not possess a proper cell 

 the animal cell. wa ll, but consists of a primordial utricle and interior con- 

 tent alone. Its manner of reproduction is of three kinds : 1st. From 

 germs ; 2d. By fissure ; 3d. Endogenously. Where animal cells orig- 

 inate from germs, these seem to be granules of a substance analogous to 

 fibrin, which are floating in the formative liquid. In duplication by sub- 

 division, the import of the nucleus is shown by the fact that the action 

 begins at it. It may be said of animal cells that the nucleus maintains 

 a more conspicuous relation than it does in the case of vegetable ones. 

 Reproduction in the endogenous manner is carried forward in the case of 

 these cells in the manner described in a preceding paragraph. 



OP THE CONSTRUCTION OP CELLULAR AND VASCULAR TISSUES. 



By their development and juxtaposition with one another, cells give 



Cellular tissue r * se to coirt inuous fabrics of various kinds, or cellular tissue. 



its various If the development of new cells occurs in a space where there 



is freedom from pressure, the cells maintain their original 



