248 THE OCEAN WORLD. 



the coral polyp, which have a central, perhaps a sensible organ, 

 common to all, which binds them to each other, giving a certain 

 unity to their acts. The Gorgonian polyps have no will ; the Pen- 

 natula have." 



CTENOPHORA. 



We have now reached the class of polyps which Cuvier designates 

 Hydrostatic Acalephce, and which De Blainville calls the Ciliobranchiata. 

 The body of these polyps presents marginal fringes furnished with 

 vibratile cilia, which are swimming organs. Moreover, as these 

 vibratile fringes are inserted directly over the principal canal, in 

 which the nourishing fluid circulates, they ought necessarily to help 

 in the act of respiration, by determining the renewal of the water in 

 contact with the corresponding portion of the tegumentary mem- 

 brane. 



The class may be divided into five families, namely, Callymmida, 

 Ccstidce, Callianiridce, Plenrobrachiada, and Beroidce. 



The creatures belonging to these families swarm in the deep 

 sea; they often appear quite suddenly, and in vast numbers, in 

 certain localities. 



Bcroe Forskalii (Fig. 102), has been studied with great care by 

 M. Milne-Edwards. The species inhabits the Gulf of Naples, and 

 the sea almost everywhere ; the sailors of Provence call them Sea- 

 cucumbers. The body (Fig. 102), cylindrical in form, is of a pale 

 rose colour, thickly studded with small reddish spots, so numerous 

 as to appear entirely punctured with them. It presents eight blue 

 sides, with very fine vibratile cilia, which by their reflection produce 

 all the colours of the rainbow. The substance of the body is 

 gelatinous, its appearance glass-like ; its form varies according as 

 the animal is in motion or repose. Sometimes it swells up like a 

 ball ; sometimes it reverses itself, so as to resemble a bell ; at others 

 it is elongated and cylindrical ; at its lower extremity it presents a 

 large mouth ; at its upper extremity is found a small nipple, having 

 at its base a spherical point of a reddish colour, enclosing many 

 crystalloid corpuscles, which rest upon a sort of nervous ganglion, 

 whose physiological function is not very well determined. A vast 

 stomach, considering its size, occupies the whole interior of the body 

 of the Beroe : the circulation is also much developed in this creature. 

 The circulating apparatus contains a moving fluid charged with a 

 multitude of circular, colourless globules, which flows from a vascular 

 ring round the mouth towards the summit of the body ; in the 

 interior are eight superficial canals, which flow under the ciliated 



