STRUCTURE OF ROTIFERS. 



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



as an advanced trochospJiere or more properly cephalula, and 



comparable with the larvae or cephalulae 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) which seize and masticate the food, which, 



through the rotary action of the velum, passes 



down the bnccal channel or mouth-opening, and 



lodges within the mastax. The so-called sali- 



vary glands are 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 Cieca, while the intestine ends in a rectum 



and cloaca, the latter opening at the base of 



the tail. In Jfotommata, 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. 



Fi 



