368 THE INFUSORIA 



Another noteworthy feature of the mouth region are the tracts 

 of trichocysts which are occasionally seen (Dileptits, Amphileptus) 

 leading from the anterior part of the prostomial lobe to the mouth. 

 The specialisations of cilia and other structures in the region of 

 the mouth of these animals are so numerous, however, that a 

 description of the conditions met with in each genus would be 

 necessary to do justice to the subject. 



There can be no doubt that in some forms, such as Blepharocorys 

 (Fig. 4), Nyctotherus (Fig. 56), etc., a definite cytopyge or cell-anus 

 does occur, and in others (certain species of Entodinium) the anus 

 opens into a groove-like depression of the surface. As a general 

 rule, however, there is no definite opening of this character and 

 the undigested parts of the food are simply pushed through the 

 cortex at some particular region of the body. 



CILIA, CIRRI, MEMBRANES, AND TENTACLES. 



In all the Heterokaryota there are to be found delicate proto- 

 plasmic processes from the general surface of the body, which 

 perform the function of locomotion and ingestion of food or of 

 sensation. These may have the form of very delicate and short 

 whip-like threads, which are called cilia ; coarse, blunt, or pointed 

 processes, which are called cirri ; expanded, flattened membranes ; or 

 the remarkable suckers and tentacles of the Acinetaria. 



It is not an unreasonable hypothesis that in the ancestral forms 

 the processes had the form of cilia, and that in the process of differentia- 

 tion of the Heterokaryote body, the cilia in certain regions became 

 fused together to form cirri and membranes, or differentiated to 

 form suckers and tentacles. The view that the ciliated body was 

 the most primitive is supported by the facts that the genera of the 

 class Ciliata, which are apparently the simplest in general structure, 

 exhibit no modification of their ciliary apparatus, and that in the 

 highly differentiated Acinetaria the free-swimming buds are always 

 provided with bands or tracts of unmodified cilia until they assume 

 the sedentary habit. 



The cilia in their simplest form are composed of the clearest 

 and most homogeneous kind of protoplasm, in which no granules 

 nor fibrils of any kind can be discovered. They spring from the 

 pellicle, and, as Butschli has clearly shown, are continuous with it. 

 In many forms they undoubtedly appear to penetrate through the 

 alveolar layer into the subjacent medulla, but this appearance can 

 be best accounted for by the view that they are usually supported 

 and influenced by a specialised thread of the cortical protoplasm 

 attached to their seat of origin. They rarely exceed the extreme 

 length of 16 /z, and they vary from O'l //, to 0'3 p in diameter. 



