96 ZOOPHYTES. 



any other than the passive faculty of merely receiving such nutrition as 

 shall promote its own advances towards maturity. 



Whatever be the common rules adapted to strike the senses, neither 

 age nor dimensions will prove perfection, both being relative characters. 



The hydra perjDetuates its race after principles adverse to those usual 

 arrangements of Nature, of which we are enabled to judge. Its progeny 

 is originating at the earliest visible stage of the parent, and this progeny, 

 while still incorporated with that parent, is giving birth to offspring. The 

 descendants to a remote generation are in the exact resemblance of the 

 original hydra, their progenitor. They inherit its form and its properties 

 unchanged. 



My observations on the group investing the shell of the Solen, were 

 continued as far as practicable, during two years and eight months : and 

 on another colony and its descendants, they were continued for six years. 

 Many specimens have been assumed and preserved besides, on different 

 occasions, during the last twenty-three years at least. 



From what has been said, the mode of increment, whereby the Sertu- 

 larian and other compound zoophytes are augmented, will be the more 

 easily understood, making some allowance for the diversities of structure. 



The following conclusions may be deduced from the preceding nar- 

 rative : — 



I. The nature of the Hydra tiiha is nearly identified with that of the 

 hydra or polypus of the fresh-waters of Scotland. 



II. The body consists of a dilatable conical sac, with a marginal row 

 of tentacula around the disc, which are capable of extending five times 

 the length of the body. 



III. It feeds voraciously, and like the Actinia, rejects the undigested 

 residue by the mouth, which is in the centre of the disc. 



IV. It can endure long protracted abstinence, under which the size 

 o-radually diminishes, but is suddenly restored by sustenance, and it sur- 

 vives during years. 



V. It is extremely prolific ; and propagates by gemmation or the 

 budding of the offspring from its side. 



