ELEMENT ART STRUCTURE OF ORGANIZED BODIES. 15 



these, cells will by and by be formed, as at c and d> which still 

 surround the nucleus intimately, and are very thin in the 

 walls. These cells expand by growth, and their walls, at the 

 same time, become thicker. The nuclei also grow in a very 

 slight degree for a while. The 

 cells now contain a clear fluid, 

 then a granular precipitate, 

 which generally first forms it- 

 self around the nucleus, as at 

 e, figure 4, for example. In the 

 old cells young cells occasion- 

 ally arise. By and by cavities 

 or canals are formed in the car- 

 tilages in a way w r hich has not 

 yet been investigated with suffi- 

 cient care, through which these 



vessels also take their course. Fig> 4 represents the branchial 

 If, after this epoch,, any new cartilage of a very young larva of 

 cells are produced, we may pre- the frog. The lower edge of the 

 sume that their evolution takes Preparation is the natural limit of 

 place, not only from the sur- t] 



face of the cartilage, but also around these vascular cavities 

 and canals ; and, perhaps, it is from this circumstance that, 

 after ossification, the cells are found disposed in laminse, 

 partly concentric around the cavity of the medullary canal, 

 partly parallel with the surface of the cartilage. In the pro- 

 cess of ossification, the earth is first deposited in the cytoblas- 

 tema of the cartilage. The cells of the cartilage, at the same 

 time, suffer a remarkable change, which seems to consist in 

 their becoming elongated in different directions into hollow 

 processes or canals, and thus acquiring a stellated appearance 

 (stellated cells). The nuclei of the cells, during this process, 

 are absorbed. At length, and finally, the cells themselves, and 

 the canals proceeding from them, appear to become filled with 

 calcareous earth. 



[ 53. CELLULAR TISSUE. The cytoblastema of the cellular 

 le is a structureless, gelatinous looking, transparent sub- 

 stance, uot unlike the vitreous humour of the eye. Within 

 this arise small round granular-looking cells, furnished with 

 nuc 1 ".) Here, too, the nucleus appears to be the 



part first formed, the cell being developed around it. As the 



