218 



COMPARATIVE ANATOMY 



which are slightly longer than elsewhere, and completely 

 clothe the external surface of the body. They extend also 

 into the mouth and line the narrow tube through which the 

 mouth opens into the endoplasm. Examination with a very 

 high power of the microscope shows that the cilia are 

 arranged in a definite order in rows. In the posterior half 

 of the body the rows are nearly longitudinal, but in the anterior 



cv' 





47- 



Parainecium caudatum. A, a view of the entire animal ; m, mouth or cyto- 

 stome ; an, anus ; cv, contractile vacuole in diastole ; cv, contractile 

 vacuole in systole ; ma, meganucleus ; mi, micronucleus. B, the hinder 

 portion of the same animal more highly magnified to show the mouth 

 leading by a funnel-shaped cytopharynx into the endoplasm ; a food vacuole 

 is forming at the extremity of the cytopharynx ; um, undulating membrane ; 

 an, anus ; tr, trichocysts. The arrows indicate the direction of the flow of 

 the granules in the endoplasm. C, a diagrammatic view of a Paramecium 

 from the ventral surface, showing the mouth and peristomial groove and the 

 striations of the cuticle. (A and B, original ; C, after Biitschli.) 



half their course is modified in connection with the spiral 

 twist of the body, and they curve inwards towards the peri- 

 stomial groove on the ventral surface. Paramecium and its 

 near allies are placed in a group called Holotricha, characterised 

 by the uniform covering of fine cilia. 



