232 ZOOPHYTES. 



summit of the cell becomes a conical or an ovoidal prominence. It is dif- 

 ficult to render this intelligible without inspection of living specimens. 



Now, the hydra reposes in absolute quiescence. Next, when rising to 

 display itself, a percussive action is exhibited by the expanded tentacula, 

 as if they were inflicting blows on something in their vicinity. The neigh- 

 bouring visible particles are attracted apparently by a vortex, and tossed 

 about among them. Then, also, it is discovered by microscopic aid, that 

 the surface of each tentaculum, instead of presenting mere inequalities or 

 the rauricate character, distinguishing that of the hydraoid zoophytes, is 

 bordered on each side by numerous cilia, or short and stout hairs : that 

 the particles coming in contact with them are transmitted along the bor- 

 der, upwards or downwards, or from one to another : and that they are 

 finally absorbed in the central mouth of the animal. 



But this ciliated structure is to be recognised, in general, only under 

 favourable conditions, and by optical instruments of superior power and 

 quality. The effect, indeed, may be often seen while the cause is un- 

 known, insomuch that reputable observers, either from their own defective 

 vision, or ignorant of the proper means of assistance, have denied the pre- 

 sence of the cilia ascribed to such hydrse by more successful naturalists. 



Since Dr Fleming directed the notice of observers to the functions of 

 the Cilia of zoophytes, others have assigned an important office to those 

 occurring on many different animals. The reader will peruse with much 

 interest the article Cilia, by a learned anatomist, deeply versed in the 

 history of the lower tribes, Dr Sharpey, Professor of Anatomy and Physio- 

 lo<Ty in University College, London, composed for the Encyclopaedia of 

 Anatomy and Physiology. 



Doubtless, that creative power devising the wondrous structure of 

 animals, assigned some definite use to all their organs; but I know not 

 that these are yet completely disclosed to naturalists. 



In many such products, a distinct view of the hydra itself is obscured 

 by the intervention of neighbouring parts : and the minute inspection of 

 some is impracticable. 



I shall now proceed to offer a few general remarks on several genera 

 and species of the ascidian zoophytes, in as far as they seem to me to merit 



