THE CONTRACTILE VACUOLE 409 



Of particular interest are the observations of MacLennan (1933) on 

 the Ophryoscolecidae, cihates from the stomachs of cattle. The cycle of 

 the contractile vacuole was studied in both living and fixed material, in- 

 cluding the following genera: Ophryoscolex, Epidinium, Ostracodinuim, 

 Poly plastron, Eudiplodinium, and Metadinmm. In all these genera the 

 contractile vacuole is formed by the coalescence of small accessory vacu- 

 oles, just as in Eu plates, as described by Taylor and also by King, and 

 in Amoeba, as described by Metcalf . These accessory vacuoles arise from 

 the dissolving of granules which are found in sharply defined regions 

 around the contractile vacuole in Eudiplodinium and Metadinium, in a 

 narrow dorsal strip of the ectoplasm in Ostracodinium, and in the whole 

 ectoplasm in Ophryoscolex and Epidinium. If one may be permitted to 

 assume that the canals and granules in Euplotes are identical, then the 

 mode of origin of the contractile vacuole in this form is quite similar to 

 that described by MacLennan for the Ophryoscolecidae; and in its funda- 

 mental features it also resembles that reported for amoebae as well as for 

 some of the flagellates. 



In addition to the flagellates previously mentioned, Haye (1930) also 

 studied representatives of thirteen genera from four orders of ciliates. 

 In Opalina dimidiata, Isotricha prostoma, Spirostomum ambiguum, and 

 Nyctotherus cordiformis little was observed which suggests the mode 

 of origin of contractile vacuoles. Except for the fact that the walls of 

 the canals were found to contain lighter and darker zones — probably 

 because of the presence of lipoid granules — little was observed in Para- 

 mecium caudatum which may be associated with origin of vacuoles or 

 their contents. Rod-shaped entosomes were found closely packed about 

 the wall of the vacuole in Lionotus fasciola. In Stentor polymorpha the 

 wall of the vacuole is very delicate and shows only here and there a 

 granular structure; several secondary vacuoles are usually present. In 

 Blepharisma undulans, Balantidium entozoon, Polyplastron multivesi- 

 culatum, Ostracodinium gracile, and Ophrydium versatile are to be found 

 granules (entosomes) within the wall, or closely associated with the 

 wall, of the contractile vacuole. The vacuole in Epistylis plicatilis is 

 formed from numerous secondary vacuoles; no granules or entosomes are 

 to be observed. 



Von Gelei (1933) states that the vacuole system in Spathidium con- 

 sists of a primary vacuole, located usually in the posterior end of the 



