THE INFUSORIA 



205 



or entirely drawn in by the animal. In Mesodinium, there are only 

 four of these tentacles, which are arranged about the mouth (Fig. 1 15, 

 B). Tleonema has only one (A). These processes were considered so 

 important from the phylogenetic standpoint that Mereschowsky ('82) 

 formed a special group, the Suctociliata, for their reception. Neither 

 Entz, nor Stein, nor Mereschowsky, however, regarded the tentacles as 

 food-taking organs like the tentacles of the Suctoria ; the former, at 

 best, could assign to them no other function than that of assisting in 

 the capture of aliments. Maupas regarded them simply as pseudo- 

 podia, and upon them as a basis formulated his view connecting the 

 Ciliata with the Sarcodina. Butschli strongly opposed Entz's view 

 as to the origin of Suctoria and Ciliata, and believed that there is no 



Fig. 115. — Ciliata with tentacles. 

 A. Ileonema dispar Stokes. [Stokes.] B. Mesodinium pulex Clap, and Lach. [Entz.] 

 C. Hypocoma parasitica Grub. [Engelmann.] t, tentacles. 



direct connection between the tentacles of the two groups, but 

 regarded them as independent adaptations. The hypothesis advanced 

 by Butschli is that primitive forms of Suctoria (such as Hypocoma 

 (C), which has but one suctorial tentacle, and which retains its cilia 

 throughout life, the cilia being upon the ventral side only, as in 

 hypotrichous forms of Ciliata) were derived from hypotrichous 

 ciliates by the mouth portion becoming progressively drawn out into 

 a tentacle. Haeckel ('96), adopting Biitschli's view, compared the 

 simple, single, and terminal mouth-tube of a primitive suctorian with 

 the long, proboscis-like oral region of certain holotrichous ciliates, 

 such as Lacrymaria olar or L. phcenicopterus. In the closely allied 

 forms, Didinium and Mesodinium, the oral tube is not ciliated and is 

 contractile, so that when food is taken in, the tube widens into more 

 or less of a disk similar to many suctorian tentacles. In Mesodinium, 



