612 PHILOSOPHY OF ZOOLOGY. 



pears capable of subdivision. Those with ciliated ribs, 

 without tentacula, may remain under the old genus, as 

 B. ovata * and fulgens, while I include under Pleurobra- 

 chia, the Beroe pileus, which is furnished with two long 

 ciliated tentacula. 



2d Tribe. 



Buoyant air-vessels in the interior of the body. There 

 is no apparent mouth, but there are many appendages 

 which have been considered as supplying the place of 

 mouths, suckers, tentacula, arid ovaria. The following ge- 

 nera have been established : Physalia, Physsophora, Rhizo- 

 phyza, and Stephanomia. 



Class III. ZOOPHYTA. 



It is not practicable, in the present state of our know- 

 ledge, to draw a line of distinction between the animals of 

 this and of the preceding class. In general, the mouth is 

 surrounded with a circle of tentacula, seldom with a double 

 circle, by which they are distinguished from the first order ; 

 while they may be recognized as not belonging to the se- 

 cond, not only by the oral tentacula, but by the tendency 

 to become compound. It is, however, with the first order 

 of the preceding class that the resemblance is most com- 

 plete. 'The divisions of CUVIER and LAMARK, by ap- 

 pearing to be neither natural, definite, nor convenient, inti- 

 mate th extreme difficulty attending the methodical distri- 

 bution of the species. Some of the genera, as Corallina 

 and Spongia, exhibit no signs of sensibility, and but indis- 

 tinct traces of irritability. It has been proposed to form 

 these into a separate class, to be placed after the Infusoria ; 

 but, in consequence of the numerous analogies of structure 



* I have given the result of some observations on this Beroe, in Mem, 

 Soc. vol. iii. p. 400, Tab. xviii. p. 5, 4. 



