290 THE SOLIDS. 



formed and developed. The first process of multiplica- 

 tion is of a nature totally distinct from reproduction, for 

 although by it the cells are multiplied, no new ones are 

 developed. There is the same differences between the two 

 forms of cells, that having its origin in the division of a 

 single cell, and that developed from a cytoblast, as there is 

 between a slip and a seed. (See Plates XXX. and XXXI.) 



The parent or primary cells filled with the second or even 

 the third generation of new cells, may be detected in 

 abundance in almost any cartilage, but especially in the in- 

 tervertebral cartilages. It is worthy of notice that the 

 parent cells are usually situated near the centre of each 

 cartilage, while the single cells, in which the process of di- 

 vision is best seen, are mostly found outside these. From 

 this arrangement we may infer that the deeper seated cells 

 are older than those of the circumference. Whether the 

 latter are derived from the former, or whether they are 

 formed on the external margin of the cartilage, it is not easy 

 to decide ; it is most probable, however, that from the cir- 

 cumstance that the parent cells are principally found in the 

 centre of the thicker cartilages, and that it is in this situa- 

 tion that ossification commences, that the second proposition 

 is the correct one. 



It is a singular fact that the development of cartilage 

 cells may be as readily followed out in old cartilages as in 

 young, numbers of cells in process of division and in the 

 stage of parent cells being readily distinguished in each. As 

 after maturity cartilages do not undergo any increase in size 

 and as from the preceding observations it woulcl appear that 

 new cells are continually being evolved, it must be presumed 

 that the very old cells are absorbed and their place supplied by 

 the younger ones. 



In the multiplication of cartilage cells by division, a corre- 

 spondence may be traced between cartilages and many of the 

 lower tribes of animals and vegetables, especially with the 

 majority of the alga3 ; and in the development of secondary 

 cells in parent cells, they exhibit a still closer analogy with 

 certain alga? of the genera Hcematococcus and Microcystis, the 



