MICROSCOPIC FORMS OF ANIMAL LIFE. 57 



may be considered as an extensor, and the latter as a flexor, of the mal- 

 leus. By these and other muscles which cannot be so clearly distin- 

 guished, the two tinci are made to approach and recede by a perpendicular 

 motion on the hinge-joint, so that their opposing faces come into contact, 

 and their teeth bruise down the particles of food; but at the same time 

 they are carried apart and approximated laterally by the movement of the 

 free extremities of the manubria. The rami of the incus also open and 

 shut with the working of the mallei: and by the conjoint action of the 

 whole, the food is effectually comminuted in its passage downwards. 1 



448. The Alimentary Canal, which lies loose in the ' general cavity of 

 the body/ is sometimes a simple tube, passing without enlargement or con- 

 striction from the masticating apparatus to the anal orifice at the posterior 

 part of the body; whilst in other instances there is a marked distinction 

 between the stomach and intestinal tube, the former being a large globu- 

 lar dilatation immediately below the jaws, whilst the latter is cylindrical 

 and comparatively small. The alimentary canal of Rotifer (Fig. 310) 

 most resembles the first of these types, but presents a dilatation (I) close 

 to the anal orifice, which may be considered as a cloaca; that of BracM- 

 onus (Fig. 309) is rather formed upon the second. Connected with the 

 alimentary canal are various glandular appendages, more or less devel- 

 oped; sometimes clustering round its walls as a mass of separate follicles, 

 which seems to be the condition of the glandular investment (g) of the 

 alimentary canal in Rotifer ; in other cases having the form of caecal 

 tubuli. Some of these open into the stomach close to the termination of 

 the oesophagus, and have been supposed to be salivary or pancreatic in 

 their character, whilst others, which discharge their secretion into the 

 intestinal tube, have been regarded, and probably with correctness, as the 

 rudiment of a liver. In the genus Asplanchna (Gosse), there is a wide 

 departure from the ordinary Rotifer type; as the species belonging to it 

 have neither intestine nor anus. The stomach consists of a large bag at 

 the end of the gullet, about which, when the animals are quiet, the ovary 

 is bent in a horseshoe form. The indigestible matters are ejected through 

 the mouth. The curious absence of any digestive apparatus in the males 

 of this group, will be presently noticed ( 450). 2 



449. There does not appear to be any special Circulating apparatus in 

 these animals; but the fluid which is contained in the perivisceral cavity 

 is probably to be regarded as nutritive in its character; and its aeration 

 is provided for by a peculiar apparatus, which seems to be a rudimentary 

 iorm of the ' water- vascular system/ that attains a high development in 

 the class of Worms. On either side of the body there is usually to be 

 observed a long flexuous tube (Fig. 309), which extends from a contrac- 

 tile vessel common to both and opening into the cloaca (Fig. 310, i, i), 

 towards the anterior region of the body, where it frequently subdivides 

 into branches, one of which may arch over towards its opposite sides, and 

 inosculate with a corresponding branch from its tube. Attached to each 

 of these tubes are a number of peculiar organs (usually from two to eight 

 on each side), in which a trembling movement is seen, very like that of 

 a flickering flame; these appear to be pear-shaped sacs, attached by 

 hollow stalks to the main tube, and each having a flagelliform cilium in 



1 See also the description of the mastax of Melicerta ringens and Conochilus by 

 Mr. Bedwell in " Journ. of Roy. Micr. Soc.," Vol. i. (1878), p. 176. 



2 See Brightwell in "Ann. Nat. His.," Ser. 2, Vol. ii. (1848), p. 153; Dalrymple 

 in "Philos. Trans." (1849), p. 339; and Gosse in "Ann. Nat. Hist.," Ser. 2, Vols. 

 iii. (1848), p. 518; vi. (1850), p. 18; and viii. (1851), p. 198. 



