142 ZOOPHYTES. 



Although many hydrse of the Sertularise may survive that progressive 

 increment of the specimen adding to their numbers, this is utterly pre- 

 cluded in the Alcyonic masses, covered by a single stratum of asteroid 

 hydrse, not half an inch high, while the mass consists of half a cubic foot 

 in quantity. All the lower generations are overwhelmed by those above 

 them. If I rightly understand the nature of zoophytes exceeding a single 

 animated stratum, they are enlarged by extension above, not by accessions 

 below. 



The difference between the nascent Sertularia and the adult is often 

 so great, that, to pronounce their identity would be fallacious. It is the 

 same with other zoophytes. No one could recognise the Cristatella in the 

 hydra quitting the ovum, more than the Botryllus, though not yet in- 

 cluded in this class, in the early stages of its simple ascidian formation. 



Among the adults themselves, there is also sometimes such a discre- 

 pancy, that practised observers may enumerate several as distinct species, 

 which truly concentrate in one. Farther still, the naturalist may delude 

 himself in comparing the dead with the living subject. Parts of the latter 

 disappear with the fulfilment of their functions ; parts of the former are 

 obliterated. If features alter after an inexplicable manner during life, it 

 is not surprising that greater changes accompany its cessation. 



Thus the vigorous subsistence and the decay of the Sertularise may 

 occasionally manifest anomalies, precluding all theories on their original 

 formation and exact definitions of their organic structure : each discloses 

 some peculiarity unseen in the other. The naturalist will vainly seek those 

 vivid colours decorating some of the most beautiful subjects, unless amidst 

 the waters of congenial salubrity. If framing his system on the arti- 

 culations, whirls, grooves and notches exposed by transparence in decay, 

 he will find few such guides in vigorous specimens, where they are ren- 

 dered obscure or indefinite by the opacity of the neighbouring parts, and 

 only to be shown by death. Neither shall he find in the decayed pro- 

 ducts whereon most systems repose, those transparent campanulate cells 

 whither their timorous tenants can retreat for protection, together with those 

 singular and varied prolific vesicles once loading the most luxuriant pro- 



