PAEAMECIUM 5 



rapid movements serve both for locomotion and 

 for the ingestion of food. 



c. The ' myophan layer ' is the deeper layer of ectosarc, 



characterised by its longitudinal striation, which 

 varies in distinctness with the movements of the 

 animal. The striated appearance is probably due 

 to a longitudinal wrinkling of the inner surface 

 of the ectosarc. 



d. The trichocysts are minute oval sacs arranged side 



by ^eide in the deeper part of the ectosarc, 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 trichocysts, and project on the sur- 

 face beyond the cilia. They are protective and 

 offensive weapons. 



e. Two pulsating vacuoles are situated in the sub- 



stance of the ectosarc 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 they be- 

 come stellate, and canals can then be seen 

 radiating from them. They also open to the 

 exterior at the same moment. 



f. The oral groove runs obliquely backwards along the 



ventral surface from near the anterior end to the 

 mouth, which is placed a little behind the middle 

 of the length of the animal. Its cilia are directed 

 towards the mouth and drive water and food- 

 particles into it. 



g. The mouth is an oval aperture in the ectosarc at 



the hinder end of the oral groove, through which 

 the food passes into the endosarc. 



h. The anus is an aperture between the mouth and 

 the hinder end of the body. It is visible only at 

 the moment of extrusion of faecal matter. 



