104 THE INVERTEBRATA 



Strong membranellae, and are naked on the rest of the body, save some- 

 times for a few cilia or patches of cirri. 



Tintinnidiiim (Fig. 86 C). (Tintinnina.) Cup-shaped; anchored by 

 an aboral process into a chitinoid case. In fresh waters and marine. 



Entodinium (Fig. S6B). (Entodiniomorpha.) With three posterior 

 processes, of which the largest is said to serve as a rudder. In the 

 rumen and reticulum of sheep and oxen. Like others of the tribe, 

 these organisms are present in such numbers that they are believed 

 to be symbionts which play a part in the nutrition of the host, 

 rendering the vegetable food more easily assimilable by feeding on it 

 and being in turn digested further on in the alimentary canal . Infection 

 of the host is probably by cysts on grass. 



Order HYPOTRICHA 

 Ciliata with depressed body; a gullet, permanently open and pro- 

 vided with undulating membranes; an adoral wreath, curving clock- 

 wise ; the dorsal cilia represented only by a few stiff hairs ; and on the 

 ventral side usually an elaborate system of cirri and other ciliary 

 organs. 



The animals can swim but spend much of their time crawling over 

 solid objects by means of the cirri. 



Stylonichia (Figs. 89, 90). A typical example. Common in in- 

 fusions. 



Kerona. With a less highly developed ciliary system than Styloni- 

 chia. Ectoparasitic on Hydra. 



Order PERITRICHA 

 Ciliata, for the most part permanently fixed by the aboral surface; 

 with a gullet, permanently open and provided with undulating mem- 

 brane; an adoral wreath, curving counter-clockwise; and on the rest 

 of the body no cilia, save those of an aboral ring in the free-swimming 

 species and stages. 



The conjugation of members of this group has been discussed on 

 p. 28, their morphology on pp.97, 98. The anus and contractile vacuole 

 open into the deep vestibule. The meganucleus is horseshoe-shaped. 



Trichodina (Fig. 86 D). Dice-box shaped ; with aboral ring of cilia 

 for swimming, enclosing a ring of hooks for temporary attachment. 

 Ectoparasitic on Hydra and other animals. 



Vorticella (Figs. 2, 91). Shaped like a solid, inverted bell, with, in 

 place of the handle, a stalk which consists of a prolongation of the 

 body, and is clad in a cuticle and contractile by means of a myoneme. 

 Solitary. In fresh waters and marine. 



Carchesiiim (Fig. 92). As Vorticelhy but colonial. In fresh waters. 



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