112 



ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 



by a consistent mucous envelope ; so that we may find two, three, four, or a 

 larger number, clustered together within a well-defined investment, which has 

 tenacity enough to prevent them from separating. Of this we have a good 

 example in Coccochloris cyslifera (Fig. 16) ; and a yet more remarkable one 

 in Hematococcus sanguineus (Fig. 17). The cells forming such masses of 

 vegetation may be likened to those of Cartilage, which are similarly enveloped 

 by an intercellular substance, and which present the same binary method of 

 multiplication ( 129). In the Confervas we find the cells, which are succes- 

 sively produced in this manner, remaining in connection with each other, so 

 as to form articulated filaments. The terminal cell of each filament is con- 

 tinually undergoing subdivision in the manner just described, and thus the 

 filament is elongated ; whilst other cells produce regular reproductive granules, 

 which are set free by an opening that forms in the cell-wall, and which devel- 

 ope themselves into new individuals without any further aid from the parent 

 structure, in the manner already described. The difference between these 

 two modes of propagation seems to have reference to the age and degree of 

 development of the cell ; the binary division being characteristic of cells which 

 are in a growing state, and being destined to extend the original structure ; 

 whilst the formation and emission of a number of reproductive granules is the 

 function of the mature cell, and is destined to give origin to new individuals. 

 These processes are* analogous in the higher plants, the first to the develop- 

 ment of leaf-buds, the second to the production of seeds. In the Nostoc we 

 find the moniliform filaments, which are composed of a linear series of cells, 

 invested by dense gelatinous sheaths of definite extent, looking almost like 



Fig. 17. 



Hemntorcicc-i/s sanguineits in various stages of development , a, a single cell, enclosed in its mucous 

 envelope ; b, c, clusters formed by division of parent-cell ; il, more numerous cluster, ils component cells 

 in various stages of division ; e, large mass of young cells, formed by continuance of the same process, 

 and enclosed within common gelatinous envelope. 



large parent-cells (Fig. 18, n) ; and the extension of the filaments may so dis- 

 tend their sheaths as to give them the appearance of capacious globular cells 

 (Fig. 18, A). There is reason to believe that the long convoluted filaments 

 then separate into a cluster of shorter ones, each having its own share of the 

 mucous envelope. 



126. The history of the Animal cell, in its simplest form, is precisely that 

 of the Vegetable cell of the lowest kind. It lives for itself and by itself, and 



