CELL FORMATION. 531 



in this manner minute tubular structures are formed. 

 Another mode is : cells aggregate into a mass, and at the 

 point of contact run into each other, thus producing a 

 multilocular cavity ; see No. 9. Glandular structures are 

 formed in this way. Membrane is formed of a- deposit from 

 the cytoblastema; before the cell-membrane is formed, the 

 substance from the cytoblastema coalesces with those par- 

 ticles close at hand, thus forming a delicate film-like 

 membrane. This membrane Professor T. Wharton Jones 

 calls endosmotic, or retentive membrane. We may have 

 the cells coalesce to form a filament or fibre. The nucleus 

 may disappear, or form another structure. Where regc. 

 ne rat ion of tissue is proceeding, there is found a larger 

 number of granules. 



Multiplication of Cells. Cells may be formed in cyto- 

 blastema independent of any pre-existing cells; this is 

 cited as an instance of that mysterious agency designated 

 spontaneous generation. As an example of independent 

 formation, we may instance the epithelium and epidermoid 

 cells, corpuscles of the blood, and other juices of the body. 

 Cells are formed from cells in three ways. First, there is 

 gemmiparous generation, that is to say, sprouts occur from 

 previous cells and become detached, forming in their turn 

 cells; this is also termed exogenous generation, inasmuch 

 as the process takes place from the exterior. Endogenous 

 generation is the second mode, and by it is meant that one 

 cell is formed within the body, as it were, of the parent 

 cell. The third manner is denominated fissiparous gene- 

 ration, and is where one cell becomes constricted, and even- 

 tually, at the point of constriction, divides into two. Of 

 these three kinds or modes of multiplication, one only is 

 found to occur in animals it is the endogenous. The 

 exogenous is only seen in the lowest plants. Fissiparous 

 generation occurs in vegetables, and has been supposed by 

 some to occur in animals also. The most striking example 

 of endogenous generation that can be adduced, is that 

 which takes place in the ovum of animals or birds. The 

 first part formed of the ovum is the germinal cell, in the 

 centre of the yolk ; this approaches the surface, is dis- 

 solved, and there is then developed a new cell, which is 

 called the embryo cell, from which is generated a numerous 



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