160 ZOOPHYTES. 



Such prominences result from contraction of the parts then becoming 

 conical, as the summit of the cone opens in the form of the four circular 

 arcs, which is the larger orifice, of an individual Ascidia, in itself a low pro- 

 jection ; it is scarcely elevated above the level of the neighbouring surface. 



Along with the numerous orifices now opened, were interspersed 

 numerous circular or elliptical deeper depressions. 



Such was the general aspect of this gelatinous, consistent, suspended 

 mass. 



But inspected more narrowly, the whole surface was composed of 

 systems composed of ascidise, as above described, yet less definite than in 

 the preceding special examples. Equal regularity in the arrangement of 

 those more distinct could be rarely detected. The deeper depressions 

 proved to be the central orifice, around which the systems were disposed, 

 either circularly or elliptically. The figure of each seems reciprocally de- 

 pendent on that of the others, but which is the primary regulator, seems 

 uncertain. — Fig. 12. 



Only a single orifice of the two peculiar to ascidia* being exposed in 

 these component ascidia?, the others must have communicated with the 

 central cavity of the system. 



Though I describe the orifice as consisting of the union of four hol- 

 low circular arcs, it is probable that an entire, uninterrupted circle forms by 

 their extreme distension. As the orifices open, a strong current carries the 

 neighbouring particles of muddy matter towards them, when absorption 

 follows. In its previous abode it had not been idle, for now a quantity of 

 laro-e ovoidal pellets, quickly covering the bottom of the new vessel, proved 

 both the absorption of the mud, and identified this large and shapeless 

 mass as of kindred nature to the ascidian tribe. 



The vast aggregate of animals composing such a mass, all at once in 

 activity, completely depurated the turbid element. 



Several discrepancies distinguished this specimen from the substance 

 overspreading the three shells. They were in correspondence as compound 

 ascidia;. 



The single Ascidia itself, though thus diffusing to an indefinite ex- 

 tent in systems composed of indefinite numbers, does not exceed a line 



