420 GENERAL HISTORY OF THE INFrSORlA. 



a sort of subsidiary stomach, where the digestive process is finally completed. 

 Still it is not possible to establish all the minute homological relations be- 

 tween these animals and those of the vertebrate class. The intestine, like 

 the stomach, has a limiting membrane, possibly muscular, and is lined by a 

 ciliated epithelium which, unlike that of the stomach, is not coloured, and 

 its cells less easily detected. It is capable of very great distension. The 

 rectum commonly ends in, or, it may be said, expands into, a globular sac, 

 which, from its likewise receiving the eggs from the 0"sdducts opening into it, 

 is analogous to the cloaca of birds (XXXYIII. 26 i). This cloaca has a 

 fine, transparent wall, and opens, posteriorly or dorsally, at the base of the 

 pseudopodium, or, where this segment is absent, near the extremity of the 

 body, by an outlet usually called the anus. 



The cloaca is particularly dilatable ; for sometimes it is much loaded with 

 accumulated faecal matter, and at others is distended by one or more of the 

 enormous eggs the Rotatoria habitually produce. In discharging an egg, or 

 in emptying itself of other matters, the cloaca is everted and thrust out 

 through its external orifice. 



From the mode in which the walls are drawn into longitudinal and circular 

 folds, as exemplified in Nofommata cenfrura (XXXVIII. 26), Leydig is in- 

 duced to admit the presence of muscular fibrils regularly disposed in the 

 two corresponding directions. Moreover the manner in Avhich the cloacal 

 orifice is closed, after the extrusion of any mass, indicates, in this author's 

 opinion, a sjDhincter power, and consequently the presence of muscular fibres 

 around it. The contraction of the entire canal on itself is sometimes so great 

 that it is only manifest by a streak. 



A most remarkable structural exception is met with among certain female 

 Rotatoria, viz. the entire absence of an intestine and anus. It prevails in 

 the genus Asplanchna (Gosse), in the Notommata SieholdU (Leydig) (probably 

 in N. Syrinx), in Ascomorpha Helvetica (Periy), and in A. Germanica (Perty) 

 (XXXYI. 9 ; XXXVII. 32 ; XXXYIII. 28). This want of a discharging 

 posterior outlet necessitates the rejection of excrementitious matters from the 

 stomach through the mouth. 



This structure is so very exceptional and peculiar, that Prof. "Williamson 

 is not prepared, without further evidence than has yet been advanced, to 

 admit it as time of any Rotifera. It is, he writes {in lit.) contraiy to pro- 

 bability, and, if established, would induce him to exclude the animals so 

 organized from that class. 



Reception of Food — its Deglutition, &c. — The food of the Rotatoria, as 

 before noticed, is attracted towards the mouth by the vortex caused by the 

 rotation of the cilia crowning the head. An exceptional means of prehension 

 is seen in those Rotatoria which protrude their jaws beyond the mouth, using 

 them as pincers or forceps to seize any larger prey. ^' In general," wiites 

 Mr. Gosse {Phil. Trans. 1856, p. 429), " the ciliaiy vortices are sufiicient to 

 bring the prey Tsithin the buccal funnel (pharynx) ; but in several genera 

 of the family Euchlanidota, as Metopidia, Colunis, Monura, and Steplianops, 

 there is a curious accessory organ, which aids in the captui'e of the prey ; at 

 least I am sure it is so employed in several species of Metopidia. Thus in 

 M. acuminata the frontal region is formed by an arched fleshy process occi- 

 pitally, which is approached by a small one on the ' mental ' side ; and be- 

 tween these is the wide entrance of the buccal funnel. The occipital process 

 is protected by a horny crystalline plate, forming a segment of a sphere, and, 

 when viewed laterally, taking the appearance of a curved horn. It can be 

 partially protruded and retracted, and also bent do^Ti to meet the mental 

 lobe. This apparatus, when the animal is taking food, is kept in vigorous 



