SCOLECIDA. 



125 



partitions. The integument is usuiilly provided with bundles of 

 muscular fibres taking a longitudinal and transverse direction. In 

 the free forms the anterior ciliated disc acts somewhat like the pro- 

 peller of a screw-steamer in driving the organism through the water 

 — in all cases it has the action of producing currents in the water l;iy 

 which particles of food ai'e brought to the mouth. The posteiior 

 end of the body is usually developed in the free forms into a kind 

 of tail or foot (fig. 79, A), which may take the shape of a kind of 

 pincers or of a little suctorial disc. 



As regards their internal anatomy, in the females of almost all 



Fig. 79. — Rotifera. A, Diagrammatic representation of Hydaiirut senta (generalised 

 fi'om Pritcliard) : a Depression in tlie ciliated disc leading to the digestive canal ; 

 b Mouth ; c Pharyngeal buUj with masticatory apparatus ; d Stomach ; e Cloaca ; / 

 Contractile Ijladder ; (/ g Resjiiratory or water-vascular tuljcs ; h Nerve-ganglion, 

 giving tilanient to ciliated pit (/.•); o Ovary, B, Meliccrta ringens (after Gosse). 



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

 completely shut off from the general cavity of the body. The 

 mouth (tig. 79, A, h) opens into a dilated chamber or " pharyngeal 

 bulb " ((■), which contciins a complicated apparatus of horny teeth. 

 The pharynx opens into a capacious stomach (rf), continued into an 

 intestine which terminates by a chamber known as tlie "cloaca" (c), 

 which forms the common outlet for the water-vascular and genera- 

 tive systems. In both sexes there is a well-developed water-vascular 

 system consisting of a contractile clumber or bladder (_f), opening 

 into the cloaca, and giving origin to two complicated tubes which 



