PARAMECIUM. 5 



B. Structure. 



The two layers, ectosare and endosare, are much more 

 sharply defined than in Amceba. 



1. The ectosare is the comparatively firm outer layer, the 

 elasticity of which preserves the general form of the 

 body. Its deeper part is marked by longitudinal 

 or oblique ' myophan ' striations, which vary in 

 distinctness with the movements of the animal, and 

 are probably due to longitudinal wrinkling of the 

 inner surface of the ectosare. 



a. The cuticle is the delicate superficial and stiffer 



layer, serving as a protective covering for the 

 underlying protoplasm, of which it is the dif- 

 ferentiated external layer. 



b. The cilia are very numerous delicate vibratile fila- 



ments arising from the layer of ectosare imme- 

 diately beneath the cuticle, through which latter 

 they project. They are of uniform size over the 

 entire surface, and extend into the oral groove. 

 Their rapid movements serve both for locomo- 

 tion and for the ingestion of food. 



c. The triehocysts are minute oval sacs arranged side 



by side in the deeper part of the ectosare, per- 

 pendicular to the surface, and in such numbers 

 as to form an obvious layer. When the animal 

 is irritated a stiffish thread can be shot out from 

 each of these triehocysts, and project on the sur- 

 face beyond the cilia. They are ' protective and 

 offensive weapons. 



d. Two pulsating vacuoles are situated in the sub- 



stance of the ectosare of the dorsal or aboral 

 region, one at about a third of the animal's length 

 from each end. In diastole they are nearly 

 spherical, but at the moment of systole, or con- 

 traction, they become stellate, and canals can 

 then be seen radiating from them. They also 

 ■ open to the exterior at the same moment. 



