STRUCTURE OF ROTIFERS. 



177 



not over six, segments. A Rotifer may, in fact, be regarded 

 as an advanced trochospTiere or more properly cephalula, and 

 comparable with the larvse or cephalulre of mollusks, Poly- 

 zoa, Brachiopoda and the Annelids. The alimentary canal 

 consists of a funnel-like cavity, the mouth, which may 

 be central, or situated on one side of the head ; it leads 

 to the mastax or pharynx-like muscular sac, supporting 

 a complicated set of chitinous teeth within (malleus 

 and incus) Avhich seize and masticate the food, which, 

 through the rotary action of the velum, passes 

 down the buccal channel or mouth-opening, and 

 lodges within the mastax. The so-called sali- 

 vary glands arc two large, clear, vesicular 

 glands, which are attached to the funnel and 

 rest on the summit of the mastax. The latter 

 opens into the oesophagus, "a membranous 

 tube, capable of great expansion and contraction, 

 but varying much in length and diameter in 

 different genera." Gosse also states that a cur- 

 rent of water appears to be almost constantly 

 setting through the funnel and mastax, and 

 thence through the oesophagus into the stomach 

 the latter is quite large, and provided with so- 

 called "pancreatic" glands, emptying into the 

 anterior end. There are also hepatic follicles 

 and caeca, while the intestine ends in a rectum 

 and cloaca, the latter opening at the base of 

 the tail. In Notommatd, the digestive canal 

 ends in a blind sac, and in such male Rotifers 

 as are known, there is no digestive cavity, the 

 canal being represented by a solid thread. 



There are no vascular or respiratory organs, but 

 a system of long, convoluted excretory tubes, 

 one on each side of the body, which, as in the Trematodes 

 and Cestodes, unite in a common, large contractile vesicle 

 which opens into the end of the intestine. These tubes, 

 which are in places ciliated, correspond to the segmental or- 

 gans of Annelids ; they are open at the end, the cavity of 

 the tubes thus communicating with the body-cavity. 



Fig. V&. 



ma-- 



