SCOLECIDA. 117 



anterior ciliated disk acts somewhat like the propeller of a 

 screw-steamer in driving the organism through the water in 

 all cases it has the action of producing currents in the water 

 by which particles of food are brought to the mouth. The 

 posterior end of the body is usually developed in the free 

 forms into a kind of tail or foot (Fig. 43, A), which may take 

 the shape of a kind of pincers or of a little suctorial disk. 



As regards their internal anatomy, in the females of almost 

 all the Rotifera there is a well-developed alimentary canal, 

 which is completely shut off from the general cavity of the 

 body. The mouth (Fig. 43, A b) opens into a dilated cham- 

 ber (c), which contains a complicated apparatus of horny 

 teeth. This in turn opens into a capacious stomach (c?), con- 

 tinued into an intestine which terminates by a chamber known 

 as the "cloaca" (e), which forms the common outlet for the 

 water-vascular and generative systems. In both sexes there 

 is a well-developed water-vascular system consisting of a con- 

 tractile chamber or bladder (/"), opening into the cloaca, and 

 giving origin to two complicated tubes which are known as 

 the "respiratory tubes" (g </), and which terminate near the 

 anterior end of the body, apparently by blind extremities. 

 The nervous system is in the form of a large double ganglion 

 placed above the gullet, and having one or two eye-specks 

 placed upon it. The ovaries (o) constitute conspicuous organs 

 in the female Rotifera, but in summer the young Rotifers ap- 

 pear to be produced by the females without having access to 

 the males. 



The Rotifera were long confounded with the Infusoria, in 

 consequence of their great similarity in external appearance. 

 They are, however, of an obviously much higher grade of 

 structure. One of the most remarkable phenomena presented 

 by the Rotifera is found in the undoubted fact that, in spite 

 of their complex organization and aquatic habits, they can be 

 dried, and again brought to life by the addition of a little 

 water, and that this desiccation and restoration to life can be 

 apparently repeated many times in succession without injury. 



