STRUCTURE OF ROTIFERS. 



135 



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



as an advanced trochosphere or more properly cephalula, and 



comparable with the larvae or cephalulge 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 buccal 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 caeca, while the intestine ends in a rectum 



and cloaca, the latter opening at the base of 



the tail. In Notominata, 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 ^(ji?'^ 6 8 Jg Ve 

 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. 



f iK 93. _ Ro . 



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