Order 2. HYDROSTATICA. 671 



of the other ; but they can in every case be separated witliout injury to the life of either. Tlicy 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 sing'ular animals are inhabitants of the tropical and southern seas ; and we are indebted for most of wbat 

 we know concerning them to JIM. Quoy ana Gaymard.] The following' are their distinctions as grounds of 

 classification : — 



Diplnjes proper, in whidi the two individuals are similar and pyramidal, with a few points round the apnrture, 

 which is in the base of the pyramid. 



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



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



Ciibo'ides: the received small, and bell-shaped ; the receiver larg^er, and square. 



Navicula : the receiver bell-shaped, and the received larg^e, but something^ iu 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 i^ometimes 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 dwelhng.] 



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 frequentl)'' 

 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 CARNOSI— (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; 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. This aperture, which is of course both mouth 

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

 a proper mendjrane of its own ; and bctv\ ecu tfnis and the external skin there is a rather com- 

 plicated, but obscurely known organization, consisting of vertical and fibrous leaflets, to >\hich 



