48 



LECTURE III. 



disposed in four masses, and inserted into the longitudinal or poste- 

 rior portion, which may be regarded as the rudimental jaw. The 

 efficacy of these instruments in tearing to fragments the objects swal- 

 lowed up may be easily discerned in the living animal through its 

 transparent parietes. 



The condition of the alimentary organs differs in the two sexes of 

 the Rotifera. In the minute males there is a simple digestive sac, 

 without intestine or anus ; and those parts are absent, according to 

 Gosse, in the female also of his Asplanchna priodonta* In the 

 females of all the species pi'eviously observed the alimentary canal is 

 a more or less simple tube {fig- 20, f,g, /?), commonly extending lon- 

 gitudinally through the well-developed abdominal cavity, to terminate 

 by a cloacal outlet (Ji) at the hinder end of the body, generally above 

 the base of the sheath of the claspers. In the loricate Tubicolaria 

 and Melicei'ta the intestine is bent and the anus opens far forwards. 

 The canal is sometimes wider, sometimes narrower, sometimes with 

 (Euchlanis, Bracldonus) and sometimes without {Philodina) a 

 constriction indicative of the stomach : this cavity is 

 usually well marked in Notommata {Jig. 20, g^ : in 

 Rotifer {fig. 21.) and Ptyura there is a distinct ter- 

 minal dilation or rectum : sometimes the intestine is 

 complicated with many caeca, as in Diglena and Mega- 

 lotrocha. The lining membrane of the alimentary 

 canal is beset with vibratile cilia, and the parietes con- 

 sist of cells, with a colourless nucleus, and with a 

 brown or green finely granular contents, which may 

 elaborate a fluid analogous to bile. Most of the Roti- 

 fers (certain species of Ichthydina being exceptions) 

 have, just behind the pharynx, or continued from the 

 stomach, two large oval glandular sacs, rarely cylin- 

 drical or bifurcated, to which sometimes filamentary 

 caeca are appended, as in Enteroplea. These secerning 

 sacs {fig. 20, i) are also lined by a ciliated epithelium, 

 Ai. canal. Rotifer, and, from the colourlcss nature of their contents, are 

 probably of the nature of pancreatic glands. 



Ehrenberg recognises a vascular system in the parallel transverse 

 slender bands which surround the body ; these are in close connec- 

 tion with the integument, and are more probably muscular. 



In most Rotifers tliere extends down each side of the body a 

 narrow band or tajniiform organ, containing a motionless vasiforra 

 canal. At the anterior part of the bands many short lateral vessels 



* XXXVI. p. 20. 



