22 THOUGHTS' ON ANIMALCULES. 



V. 



CELLS, THE ESSENTIAL ORGANS OF LIFE. 



THE interpretation of these phenomena is to be found 

 in the peculiar organisation of the Hydra: its entire 

 structure being nothing more than an aggregation of 

 cells. A vertical section of a polype (see pi. i, fig. 8), 

 shews the internal cavity or digestive sac, the relative 

 thickness of the substance of the body, and the manner 

 in which the arms are formed by a prolongation of the 

 upper part into hollow processes. The entire animal 

 consists, in fact, of a simple cavity formed of a congeries 

 of cells, for the reception and assimilation of food. The 

 cells lining the stomach select and absorb the nutritious 

 particles, and the tube then spontaneously contracts, and 

 casts out the residue of digestion. The organisation of 

 the polype is, therefore, analogous to that of the simplest 

 condition of the vegetable kingdom, the Celluloses ; for, 

 even in the large Fuci, or sea-weeds, the whole fabric 

 consists of cells. The fresh-water Conferva are merely 

 jointed films composed of cells, which contain granules 

 or lesser cells. A cell bursts, the granules escape, float 



