io4 COMPARATIVE ANATOMY AND PHYSIOLOGY. 



of its most characteristic organs (the cilia) are 

 specially modified in the neighbourhood of the 

 " mouth." In other words, we have here the first 

 sign of a correlation between the digestive orifice and 

 the organs which are locally connected with it, and 

 which are also in relation with the outer world. The 

 cilia around the mouth of Paramcecium (Fig. 3 I.) are 

 much longer than those which fringe the greater part 

 of their body, and give rise to more powerful currents, 

 by means of which food particles are floated towards 

 the orifice. 



Some of the ciliated Infusorians, such as Opalina 

 ranarum and Anoplophrya are endoparasitic, and in 

 these the mouth is lost (Fig. 51), as it is also in the 

 Gregarinida, which live in cavities rich in nutrient 

 matter, such as the intestine of the lobster, or the 



testicular re- 

 servoirs of the 

 earthworm ; in 



Pig. 51. Anoploplirya prolifera. (After Clapa- SUC ^ ^ Orms ^ 

 rede and Lachmann.) these nutri- 



ment enters 



into the substance of the cell by the mere physical 

 process of diffusion or osmosis. 



In the ectoparasitic Suctoria, where the mouth is 

 likewise lost (Fig. 3 in.), processes of the body are 

 drawn out into sucking tubes with knobbed'ends ; these 

 tubes retain the extensile and contractile power of 

 simple protoplasm, so that they are able to elongate 

 themselves in such a way as to touch their prey, 

 which is ordinarily a ciliated infusorian, and to con- 

 tract themselves so as to draw the prey nearer. The 

 knob is enabled to bore its way beneath the cuticle, 

 and then, in the words of Stein, " a very rapid stream, 

 indicated by the fatty particles which it carries, sets 

 along the axis of the tentacle, and, at its base, pours 

 into the neighbouring part of the body of the Acineta." 



