ON FOLYPS. 45 



furnished with a complete digestive canal, and approximating in 

 their general economy very superior orders of animals. These latter 

 would appear to be distinguishable by the nature of the tenta- 

 cles around the mouth, which, in all the families as yet examined, 

 we have found to be smooth or merely fringed, as they are indeed 

 in some of the tubular polyps hereafter to be noticed ; but, in the 

 more perfect species, the arms are covered with vibratile hairs or 

 cilia, forming important agents in securing prey : such have been 

 separated by Ehrenberg into a distinct class, under the title of 

 BRYOZOA, and have been recently designated by Dr. Arthur Farre, 



ClLIOBRACHIATE POLYPS. 



Further observation is necessary before the boundaries of these 

 important divisions can be accurately laid down ; we shall neverthe- 

 less, without entering upon a question foreign to our present sub- 

 ject, arrange them in conformity with the analogies of their internal 

 structure, rather than of their outward general form, and defer the 

 consideration of the ciliobrachiate division to another place. 



(63.) In the unciliated tubular polyps, the common body of 

 the animal, instead of encrusting a solid skeleton, is enclosed in a 

 horny sheath, which it traverses like the pith of a tree, follow- 

 ing all the ramifications of the branched stem of the polypary : 

 to the central part are attached, at intervals, cells opening exter- 

 nally, in which the polyps which provide nourishment for the whole 

 are lodged. 



Zoophytes of this description are readily found on our own 

 coasts, and the microscopic observer can scarcely enjoy a richer 

 treat than the examination of them affords. In order to study 

 them satisfactorily, it is necessary to be provided with several 

 glass troughs, of different depths, in which the living animals 

 immersed in their native element may be placed : in this situa- 

 tion, if the water be carefully renewed at short intervals, they will 

 live for some time. 



(64.) On examining a piece of one of these polyparies with a good 

 glass, the tubular horny envelope is seen to be filled with granular 

 matter ; and, on attentively watching it, globules will be seen moving 

 in different directions, producing a sort of circulation or cyclosis 

 very much resembling what is observable in some plants. The glo- 

 bules thus moving do not appear to be contained in vessels, but steal 

 in slow currents, ascending along the sides, and returning down the 

 middle in an opposite direction, as represented by the arrows in 

 fig- 14. 



