266 ZOOPHYTES. 



mate dimensions which they attain seem yet unknown. Their increment 

 and luxuriance are clearly dependent on situation, age, and sustenance. 

 Some are single, scarcely discernible by the eye : nor are the finer mem- 

 bers of the greater part to be recognised without resorting to the micro- 

 scope. When plentifully fed, and kept in a salubrious condition, the 

 organs previously diminishing are quickly invigorated and enlarged. 



Hundreds invest a favourable surface, in a single stratum, never to 

 be thickened : some are solitary : and masses of others are continually 

 rising. 



The mode of increment may be distinctly followed, whether by simple 

 divergence from a stem originally single, or by superposition of successive 

 strata, overwhelming the tenants of those below. 



Every zoophyte seems originally single. 



The food of the larger proportion of this extensive tribe is little 

 known. There are certain genera, however, such as the Hydra and Ac- 

 tinia, which are ravenously carnivorous ; and it is evident that the ascidian 

 genera can derive beneficial aliment from mud intermixed with water. 



Purity of the element wherein zoophytes dwell, seems more essential 

 than sustenance. Slight contamination is frequently fatal, after the brief- 

 est interval. Neither can fresh or salted water be substituted for each 

 other with impunity. Frequent humectation, and copious supplies of their 

 native element are indispensable. Privation, even for a short period, is 

 destructive of the more delicate species, for perfect desiccation is incom- 

 patible with the nature of the race. 



Many may be, nevertheless, transported considerable distances with 

 safety, in wet cloths, moistened moss, or leaves ; and there is little doubt 

 that, from the rapid transit of every thing in the present era, the natura- 

 lists of Britain might be gratified by receiving living zoophytes from the 

 coast of America or the West India Islands. Capacious glass vessels, and 

 occasional renovation of the water, would comprehend all that is neces- 

 sary for such exotics. 



Diseases are certainly induced by stagnant water, which shews the 

 necessity of frequent renewal. Exuviation is probably incident to all. In 

 some it advances profusely. 



