UYDROSTATICA. G53 



of the other; hut they can in every case he separated without injury to the life of either. Thev are 

 gelatinous and transparent, and move nearly in the same manner as the Medusae. The containing 

 animal produces from the bottom of its cavity a chaplet, which passes along a semi-canal in the con- 

 tained one, and which chaplet appears to consist of ovaries, tentacula, and suckers, analogous to those 

 of the preceding genera. 



[These singular animals are inhabitants of the tropical and southern seas ; and we are indebted for most of what 

 we know concerning them to MM. Quoy and Gaymard.] The following- are their distinctions as grounds of 

 classification : — 



Diphyes proper, in which the two individuals are similar and pyramidal, with a few points round the aperture, 

 which is in the base of the pyramid. 



Calpes, in which the received is pyramidal, and the receiver small and square. 



Abyles : the received oblong, or oval; the receiver small and bell-shaped. 



Cuboides: the received small, and bell-shaped ; the receiver larger, and square. 



Navicula: the receiver bell-shaped, and the received large, but something in the shape of a wooden shoe. 



There are other combinations besides these ; [but we know too little of the habits of the animals to be able to 

 understand the purpose of their very irregular economy. We do not even know whether any one form is adapted 

 for being only a received or a receiver, or whether the same form of animal may not be sometimes the one and 

 sometimes the other ; neither do we know when, how, or for what purpose the one takes possession of the other 

 as a dwelling.] 



THE FOURTH CLASS OF THE RADIATA — 



THE POLYPI,— 



The Polypi are so named, because the tentacula which surround their mouths have 

 a slight resemblance to the arms of the Cuttle-fish (Sepia), which was called Polypus 

 by the ancients. The form and number of these tentacula vary. The body is always 

 cylindrical, or conical, frequently without any viscera but its cavity, and frequently 

 with a visible stomach, and with intestinal tubes which are hollowed out of the sub- 

 stance of the body, as in the Medusae ; and along with these tubes ovaries are usually 

 found. The greater part of them are capable of producing new individuals by putting 

 out a sort of buds ; but they propagate also by eggs. [This twofold means of propa- 

 gation appears to answer a double purpose, — the buds being produced for the enlarge- 

 ment of an established colony, and the eggs committed to the waters for the purpose 

 of forming new ones.] The Polypi form three orders, which are again divided and 

 subdivided into families, tribes, and genera. 



THE FIRST ORDER OF THE POLYPI,— 

 THE CARN t OSI-(Fleshy Polypi). 



This order includes all those fleshy animals that have the power of fixing themselves by 

 their base; but many of them can also crawl upon that base, or detach it, and swim, or, at 

 all events, allow themselves to be moved along by the current of the water j but the motion 

 which they most usually perform is that of expanding or retracting the tentacula, and opening 

 and shutting the single aperture of the body. Tins aperture, which is of course both mouth 

 and vent, opens immediately to the stomach, which is a simple cul-de-sac. Ii has, however, 

 a proper membrane of its own; and between this and the external skin there is a rather coin- 

 plicated, but obscurely known organization, consisting of vertical and fibrous leaflets, to which 



