OF THE ROTATORLi. 421 



action. A strong vortex is produced by the ciliary wheels ; and as the 

 floating atoms whirl by, the moveable plate is thrown forward with a grasp- 

 ing motion, the fleshy head being at the same time protnided, and, when 

 the lobes are in contact, retracted. This is repeated almost every instant 

 with manifest eagerness and discrimination, the manducatory apparatus 

 working vigorously all the while. 



" The same curious organ is frequently employed in another way. It is 

 bent considerably downward ; and as the animal crawls deliberately up and 

 down the stems of aquatic plants, it is used to rake and grub, among the 

 floccose deposits, the minute Diatomacece, &c., that adhere to them." 



Having entered the mouth, it is usually rapidly conveyed along the pharynx 

 to the jaws. In those species which have the pharynx expanded into a ^' crop," 

 such as Floscularia and AspJancha, this transmission of the food is less speedy. 

 Mr. Gosse imagines the '' crop " to possess a suctorial power. He says — 

 "I think that when the animal {AsplancJina priodonta) is cognizant of food 

 brought to the mouth by the ciliary vortices, it suddenly expands the crop by 

 the action of the muscles that go from it to the skin, when the water rushing 

 into the vacuum carries in the prey. Then the network of fibres contracts 

 again, and the prey is secui'ed," 



Having reached the '' maxillary head," th€ food is " lodged " (to quote 

 Mr. Gosse's paper) " upon the * rami ' between the two ' unci.' These con- 

 jointly work upon the food, which passes on towards the tips of the ' rami,' 

 and enters the oesophagus (the proventricular tube), which opens immediately 

 beneath them." 



Having escaped the mandibular apparatus, the food is subjected to the 

 action of some digestive fluids which are poured into the portion of the ali- 

 mentary tube below, whether that portion be dilated into a distinct stomach, 

 or retain a nearly imiform calibre. How long this process of digestion need 

 be continued, we have no data to determine ; but we may conclude that the 

 time will varj^ according to the nature of the food, the condition of the animal, 

 its species, and other circumstances. In Melicerta rhigens, which has a double 

 stomach. Prof. Williamson remarks that the upper one " appears to be chiefly 

 a receptacle for the food. From time to time, especially w^hen the \iscus is 

 distended, a portion of its contents pass down into the lower stomach." In 

 this the mass of food usually distending it " is constantly revohdng, — the 

 motion being due to ciliary action. This process goes on for some minutes, 

 after which the creature contracts its body, and forces the entire exuvige out 

 of the viscus into a long narrow cloaca (rectum), which terminates externally 

 by an anal outlet. As it does this, it everts a considerable portion of the 

 cloaca, thus almost bringing the cloacal outlet of the stomach to the exterior, 

 and causing, at the same time, a large transparent protuberance to be deve- 

 loped on the coiTcsponding side of its body. At other times the creatui^e can 

 draw in these appendages, so that scarcely any trace of a cloacal canal is visi- 

 ble." Mr. Gosse suggests that this protrusion, at the moment of discharge, 

 is designed " to shoot the faecal mass out of the case " (urceolus) ; for the 

 outlet is then projected above the rim. " The faeces," he adds, " are slightly 

 coherent and jelly-like, not at aU like the coloui'ed pellets of which the urce- 

 olus is built up." 



The food of the Eotatoria consists of the lower Algae, of Protozoa, Ento- 

 mostraca, other Rotifers, and even the weaker members of the same species. 

 " The stomach," remarks Mr. Gosse, " of the As])lanchna is frequently occu- 

 pied with animals ; the smaller Anurcece, as A. aculeata, A. curvicornis (?), 

 and A. stipitata (?), seem to constitute its chief food. I have taken one with 

 the species last-named in its stomach, which, after about an hoiu', was ejected 



