ROTIFERA. 303 



skin is not ciliated except in certain spots, of which the trochal 

 disc is the chief. The principal integumentary glands are the 

 cement glands of the foot, which open at the extremity of the 

 pincers and secrete the substance by which the animal is fixed. 

 The tube or urceolus, in which some Rotifera live, is pfobably a 

 secretion of the skin; it is often gelatinous, but in Melicerta it 

 consists of pellets. These pellets are formed of foreign or faecal 

 particles which are worked up and cemented together by a ciliated 

 cup on the ventral side close to the trochal disc, the cementing 

 substance being a secretion of a gland (Dr) near the ciliated cup 

 (Fig. 247). 



The body-cavity is a well-marked space, traversed as stated above 

 by a few fine connective tissue strands and filled with a clear 

 vascular fluid. As to its nature we know nothing. The generative 

 and, apparently, the renal organs are in no way connected with 

 it, so that presumably it is not coelomic. It may be a haemocoele; 

 if it is, it is the only representative of the vascular system, for 

 nothing in the shape of heart or blood-vessels are known. 



The alimentary canal (Fig. 244) is ciliated throughout. It consists 

 of a mouth leading into a muscular pharynx called the mastax, and 

 provided with a special armature the troplii. The parts of the 

 armature (see below) are in continual movement, and serve for 

 mastication. In the more predaceous forms they can be protruded 

 so as to act as jaws. Following the pharynx is a short oesophageal 

 tube ; this leads into the digestive sac or stomach. The stomach is 

 lined with large ciliated cells, which often contain green or yellow 

 pigment grains. The anterior or gastric part of this cavity is wide 

 and receives two large glandular tubes, which may be explained as 

 salivary or pancreatic glands. The posterior narrow intestinal part 

 leads into a cloacal chamber, which opens on the dorsal surface at 

 the point where the foot-like posterior region joins the anterior part 

 of the body. In some cases, e.g. Asplanchna, the intestine ends 

 blindly, and the faeces are rejected through the mouth. 



Respiration is carried on by the general surface of the body; 

 special organs are wanting. 



The muscular system is complex, being composed mainly of 

 muscular bands passing between definite points. The muscular 

 tissue is in part, at any rate, cross-striped. 



Excretory organs. The so-called respiratory canals are excretory. 

 They consist of two sinuous longitudinal canals, with fluid contents ; 

 they open into the cloaca either directly or by means of a contractile 



