706 



RADIATA. 



transparency of their textures ; and that the order Eotifera ought to constitute a separate class, and 

 to have a place in the Articulated neries. 



HOTIFERA. 



The animals of this class have usually" an elongated form, and are perfectly symmetrica] on the two 

 sides. At the anterior extremity, we observe one or more rows of vibratile cilia; these are frequently 

 arranged (as in the common Wheel Animahzcle^ Fig. 21, 5), in a circular manner, and when they are 

 in motion, an appearance of revolving wheels is produced, from which the class derives its appellation. 

 In many species we find a prolongation of the body in front, extending beyond the ciliary apparatus ; 

 this, which sometimes bears one or more red spots that are supposed to be eyes, may be regarded as a 

 head (Fig. 21, a). The body is covered with a double enyelope, both layers of which are extremely 

 thin and flexible in many species, whilst in others the outer one seems to possess a horny consistence, 

 an<] may even contain siliceous matter. In thf Stepha/iiferos Elchornii^ this is so far detached from 

 the body, as almost to form a sort of polype-cell, like that of the Bowerbankia ; and the cilia, instead 

 of being disposed in circular rows, are mounted on arms like those of a polype ; so that the whole 

 animal bears a strong resemlilance to the Bryozoa, with which it forms the connecting link. 



^ ^ The 1)uJy of the Rotifer vulgaris not being enclosed in any such 



/^ dense envelope, is capable of considerable extension, and has much 



/A";! a. of the Vermiform aspect; this is increased when a slight contraction 



nAt-\\ draws the externa) membrane into transverse wrinkles, that seem 



FY][|my------'/' to indicate the set'-ments of the trunk. The posterior extremity 



-iiJiW \^ prolonged into a tail, po=sessing three joints, which can be 



drawn up within each other. Within the external integument 

 there are four longitudinal bands running from end to end ; these 

 are probably bundles of muscular fibre, by the contraction cf 

 which the body may be shortened. On the under surface of the 

 head is a projecting orifice, which is believed to act as a syphoQ 

 for the introduction of water into the general cavity for the pur- 

 pose of respiration ; the ciliary movement being destined to bring 

 food to the mouth, which is situated between the wheels. The 

 wide lesophagus terminates in a sort of gizzard (6?), provided with 

 regular teeth at its entrance. Tliese teeth are two in number on 

 each side, and are fixed upon hard jaws, moved by powerful mus- 

 cles, so as to work between each other. All the food which is 

 swallowed is submitted to their action, before it enters the first 

 stomach, and when the cilia are in operation, these jaws are al- 

 ways in regular movement. From the first stomach or gizzard 

 there passes off, in the Rotifer, a long straight intestine (y*y,) 

 wdiich terminated without any dilatation except near its close at 

 _^j just at tbe commencement of the tail; this tube is surrounded 

 ^th Che by a glaniiular apparatus, h, which may be regarded as a liver. 

 ; "/', Ti'i'-- In many nther Tlntifera, however, we find the gizzLird opening 

 Tdi'iMr^J into a larger cavity, which may be regarded as the true digestive 

 'i')]"'''' 'stomach. Near the termination of the intestine is the oviduct, 

 ny which are extruded the eggs, k, wliich are formed in the large ovarja. Besides the longitudinal 

 muscular bands, transverse lines may be nh.^erved to cross the body at intervals, which are 

 believed by Ehrenberg to be blood-vessels, passing off from a trunk that runs along the hack, like 

 the dorsal vessel of Insects. A distinct nervous system unquestionably exists in the Rotifera; though 

 it cannot be seen in the Rotifer vulgaris so clearly as in some others of the group. 



The movements of these animals are very activt^ and varied. Sometimes they al tach themselves by 

 the tail, and set their ciliary apparatus in motion for the purpose of obtaiuing food ; in which condition 

 they bear a strong resemblance to Bryozoa. But they also swim freely about through the water, the 

 ciliary apparatus being folded up (as in Fig. 21, B), and they then resemble aquatic Worms. And 

 sometimes they crawl along a solid surface, after the manner of a Leech, Yet with all this complex 

 organization and these active powers, many Botifera may be completely ilried up, and preserved for au 



Fio, 21. — WHErr. ANiMAi,rTT.r=i 

 fl-lir'-ls expamlwi ; H, ivitll lln; \i lnil, 

 5nLH-n irij a, the h.-iid «-iili ih, ,-,, 

 ii'lieds; r, iv!iter-si|>!iiiTt 1 d, mn-.i u-ir 

 '., Nalivnry glands, / /, intestinal cuniil 

 lermiimtiou ; A, glaiidulfir app^iratus f 

 i, young ones nearly cumplete; k, egg 



