Class 1. Turbellaria. 145 



The Turbellaria live in frest-, or salt-water, or even on land in 

 damp places. By means of the ciliary movements, and by slight 

 movements of the body-muscles, they glide through the water and 



Fig. 100. Fig. 101. 



Pig. 100. Planaria Ickctea, a, fresh-water Tnrbellarian, with eTerted pharynx. — After 

 0. Smidt. 



Fig. 101. Larva of a marine Tnrbellarian, enlarged. — After Lang. 



over any foreign objects found therein. They feed upon other 

 animals, e.g., small Crustacea, which are seized by the pharynx and 

 sucked out. 



Botli terrestrial and fresi-water forms occui- in England ; of tlie latter, species 

 of tie genios Planaria (branched gut) whicli sometimes attain a length of 

 2 c/m. (Fig. 100) ai-e the best known. Many species are found in all seas. 



Class 2. Trematoda. 



The Trematodes, all of which are parasitic, are nearly allied 

 to the Turbellaria, differing from them in that the superficial cilia 

 of the larva are lost later ; they are usijally pale or inconspicuous in 

 colour. The body, which is of a firmer consistency than that of the 

 Turbellaria, is provided with a definite cuticle, which sometimes 

 bears little spines, and is furnished with a varying number of small 

 suckers, sometimes also with chitinous hooks. These adhesive 

 organs are specially developed in ecto-parasitic forms. Eyes 

 are wanting in the internal parasites, whilst in the external ones 

 they are often present. The mouth is frequently situated at the 

 base of a sucker, and usually at the anterior end of the body. It 

 leads into a pharynx with muscular walls, which acts as a 

 pumping apparatus. The pharynx is continued into the true gut; this 

 is rarely a simple sac, more often* forking into two lateral branches. 



• In the asexual generations of many forms the gut is, however, only a simple sac ; 

 in others it is entirely wanting. (See the description of Distomum hepaiicum given 

 helow). 



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