Ciliophora 403 



Two genera have been referred to the family (105): Mylestoma Kahl (Fig. 7. 42, I) 

 and Atopodiniiim Kahl (Fig. 7. 42, C). 



Family 3. Discomorphidae. The dorsal keel, which ends anteriorly in a 

 spine, sweeps back over the posterior end to the ventral surface (Fig. 7. 

 42, H). Somatic ciliation is limited to the two ventral rows, two posterior 

 tufts of cilia on the left, and a well-developed frontal band. 



Only one genus is known (105): Discomorpha Levander (Fig. 7. 42, G, H). 



Order 3. Peritrichida. The adult is usually attached either directly by 

 its aboral end or by means of a secreted stalk, or else lies within a lorica 

 which is attached to some solid surface. A number of the stalked types are 

 colonial. A few species are free-swimming and apparently have no sessile 

 stage. 



In this order, the peristome (or "epistome") is a polar disc which, seen 

 from the oral end of the body, is approximately circular (Fig. 7. 47, H). 

 Encircling the peristome counterclockwise are two or more rows of cilia 

 which usually complete a full spiral before passing through the cytostome 

 into the vestibule. Two rows of adoral cilia have been described in 

 Telotrochidhim (138) and Cyclochaeta (146); three, in Vorticella (159). 

 In all three cases, the cilia of each row are free distally but are fused 

 basally into a continuous membrane. Each row of cilia is continued into 

 the vestibule in CyclocJweta and I'orticrlla: only the inner row, in Telo- 

 trocliidiiim. Within the vestibule, a membrane may be formed by com- 

 plete fusion of cilia (the outer row of Vorticella). The outer margin of 

 the peristomial surface, which ranges from a narrow border to a broad 

 projecting shelf, often forms a contractile rim which can be constricted 

 to enclose the peristome and its ciliature. 



The vestibule receives the contents of the contractile vacuole, some- 

 times through an intermediate "reservoir" (Fig. 7. 47, H), and also the 

 luidigested materials from old food vacuoles. As in the ordinary pharynx, 

 incoming food particles also pass down the vestibule into the developing 

 food vacuole at its base. Noland and Finley (159) have noted an apparent 

 separation of incurrent and excurrent channels within the vestibule. 



The scopula (54), a differentiated area at the aboral pole, is often evi- 

 dent as a small invagination, the wall of which sometimes shows fibrils 

 or rod-like elements. In many of the sessile species withovu stalks, the 

 scopula apparently secretes some material which insures adhesion to the 

 substratvmi. In stalked species, the scopula secretes the inert matrix of 

 the stalk. The non-contractile stalk of the Epistylidae consists entirely 

 of secreted material. The stalk of the Vorticellidae contains, in addition, 

 a loosely spiral myoneme, or "stalk-muscle," which appears to be an out- 



