88 ZOOPHYTA HYDROIDA. 



ceived from an external source, and circulating throuoh the 

 whole animal, there is not merely an upward growth, but creep- 

 ing tubes, " full of the same living medullary substance with 

 the rest of the body," are projected from the base along the 

 surface of the object of fixture. " These tubes not only secure 

 it from the motion of the waves, but likewise from these rise 

 other young animals or corallines, which growing up like the 

 former, with their proper heads or organs to procure food, send 

 out other adhering tubes from below, with a further increase of 

 these many-headed branched animals ; so that in a short time 

 a whole grove of vesicular corallines is formed, as we find them 

 on oysters, and other shell-fish, when we drag for them in deep 

 water." * 



There are many facts which prove that the growth of these 

 polypidoms is very rapid, but not more so than might be anti- 

 cipated when it is remembered how vast is the number of polype 

 architects ; and no sooner is a new branch extended than it be- 

 comes almost simultaneously a support of new workers which, 

 with " toil unwearyable," add incessantly to the materials of in- 

 crease. Their duration is various : some have only a summer's 

 existence, as Campanularia geniculata ; many are probably an- 

 nual, and the epiphyllous kinds cannot at most prolong their 

 term beyond that of the weed on which they grow : but such 

 as attach themselves to rocks are probably less perishable, for 

 their size and consistency seem to indicate a greater age : it is 

 thus with the Tubularise and some of the compound Sertu- 

 lariadse. 



But the life of the polypes considered abstractedly is proba- 

 bly in no instance coetaneous with the duration of the polypi- 

 dom, for the lower parts of this become, after a time, empty of 

 pulp and lifeless, and lose the cells inhabited by the polypes, 



" Ellis and Solander's Zoophytes, p. 33. 



'* New buds and bulbs the living fibre shoots 



" On lengthening branches, and protruding roots ; 



" Or on the father's side from bursting glands 



" The adhering young its nascent form expands ; 



" In branching lines the parent-trunk adorns, 



" And parts ere long like plumage, hairs, or horns." 



Darwin's Temple of Nature, Canto Li. 

 4 



