The Life History of Tillina Magna 389 



in the furrows, and the striae truly indicate the lines of cilia inser- 

 tion. The basal granules are not situated deep in the cortical 

 plasm, but lie near the surface, almost directly under the cuticle, 

 leaving below a wide clear space of granular cortical plasm. 



A comparison of the cortical plasm and ciliary structures of 

 Tillina with those described in other forms, shows that there may 

 be considerable variation even among related types. In Para- 

 mecium caudatum and Frontonia leucas, according to Maier and 

 Schuberg, the surface of the body is divided into hexagonal or 

 rhomboidal figures. These, however, are not raised in their 

 centers as in the case of Tillina, but are hollowed out. The sides 

 of the fields are raised to surround the hollow centers, in which 

 lie the basal granules which give rise to the cilia. The papillae 

 at the edge of a section, are the raised boundaries of the hollow 

 areas, the striations on the body indicate the lines of cilia insertion. 

 Another variation is seen in the structure of Colpidium colpoda, 

 and of Lembadion, according to SchewiakofF and Biitschli. These 

 forms agree with Tillina in having raised areas, but differ in the 

 fact that the basal granules lie in the centers of the squares, not 

 at the corners, and the striae represent merely the furrows between 

 the papillae. In the case of Opalina, Bursaria, Ophryoglena and 

 Nyctotherus, according to Maier and Bessenberger, the arrange- 

 ment is the same as has already been described for Tillina. 



Below the basal granules in the cortical plasm, there is a layer 

 of clear granular protoplasm. If trichocysts are present, they 

 should be found here, but I have no evidence of their presence; 

 Gruber and Kent mention the layer of definite trichocysts in 

 Tillina, but Biitschli ('86) later correctly interpreted this as the 

 alveolar layer. Trichocysts, therefore, are unquestionably absent. 



The contractile vacuole is of the simplest type. There is one 

 large vacuole situated in the cortical plasm on the dorsal surface 

 of the posterior lobe, and communicating directly with the exte- 

 rior. There are no definite canals or reservoirs in communication 

 with the vacuole. It has a membrane and is a stable structure, 

 not being constantly reformed. 



The endoplasm is a fine granular substance containing many 

 food vacuoles. Although there is no definite basement membrane 



