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COMPARATIVE ANATOMY 



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

 half their course is modified in connection with the spiral 

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

 tomial groove on the ventral surface. Paramecium and its 



Paramecium caudatum. A, a view of the entire animal; m, mouth; an, 

 anus ; cv, contractile vacuole in diastole ; cv' ', contractile vacuole in 

 systole ; ta, macronucleus ; mi, micronucleus. B, the hinder portion of 

 the same animal more highly magnified to show the mouth leading by a 

 funnel-shaped gullet into the endoplasm ; a food vacuole is forming at the 

 extremity of the gullet ; tun, 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.) 



near allies are placed in a group called Holotricha, characterised 

 by the uniform covering of fine cilia. 



The cell-protoplasm of Paramecium is differentiated into an 

 external elastic and delicate membrane or cuticle, within this 

 is a cortical layer (ectoplasm) of relatively dense consistency, 

 and the centre of the body is occupied by a softer endoplasm. 

 The mouth, as has already been mentioned, leads by 

 way of a short ciliated tube into the endoplasm. There 

 is a large nucleus situated nearly in the middle of the 



