170 ZOOPHYTES. 



societies or groups of individuals, which are intimately approximated to 

 each other. 



III. Under both these conditions it is always rivetted by the base to 

 a foreign substance. 



IV. It propagates though the medium of a foetus, which, on evolution 

 from the integuments, resembles a minute tadpole. 



V. This tadpole, denominated Spinula, being like an ordinary pin, is 

 at first endowed with great activity, next becomes quiescent, to undergo 

 complete transformation to the state of an ascidia, wherein it remains per- 

 manently. 



I. The Botryllus verrucosus is a compound animal product, of fleshy 

 or subgelatinous consistence, permanently affixed by the base to some 

 solid substance. 



II. It consists of aggregated ascidiae united together, which are ulti- 

 mately distributed over the substance invested. 



III. The individual ascidia? are arranged in distinct groups or systems, 

 around a common central cavity ; a number of these systems constituting 

 a specimen of the Botryllus. 



IV. Each of the ascidia? subsists under an independent existence, 

 wherein distinct functions are carried on, as, first, the circulation of a san- 

 guiferous fluid ; secondly, the nutrition derived from absorption of muddy 

 matter suspended in the surrounding element. 



V. The Botryllus subsists under compound conditions, such as the 

 benefit derived from a common circulation, besides the sanguiferous sys- 

 tem peculiar to the ascidia 1 , and from nutrition benefiting the whole. 



VI. It is propagated through the medium of a foetus resembling a tad- 

 pole, like that of the Ascidia papilla, also denominated Spinula, which, 

 quitting the integuments, enjoys life, activity, and motion for an indefinite 

 period, then becomes rooted immoveably, loses the external organization, 

 and is metamorphosed to an ascidia. 



