STUDIES ON SPATHIDIUM SPATHULA 195 



of these apparently are newly formed and being transported to 

 the oral region, while others may well be trichites which have 

 been torn away during the process of prey ingestion (fig. 12). 



In view of the fact that this organism paralyzes its prey, 

 it is natural to seize upon the chief structural differentiation of 

 the oral region as the locus of the poison. But on account of 

 the problematical function of clearly defined trichocysts when 

 present, and the absence of any proof that the trichites of Spath- 

 idium are actually the seat of the poison, we prefer not to prejudge 

 the question. Though, it is true, Blochmann in particular has 

 interpreted the trichites of certain other ciliates as related to 

 poison production. The trichites of Spathidium are apparently 

 the 'Tastkorperchen,' identified by Stein in an organism which 

 probably is a Spathidium, and the 'trichocysts' noted by Maupas. 



The trichites of Spathidium obviously are comparable to 

 the rods which form a framework for the mouth in many of the 

 more generalized gymnostomatous ciUates and undoubtedly are 

 homologous with the strands comprising the highly specialized 

 seizing organ of Didinium. Thon believed that in Didinium 

 he could discriminate between trichites and 'Stabchen des 

 Reusenapparates,' but no such distinction is possible in Spath- 

 idium. The paUng of trichites suggests that the whole surface 

 of the truncated anterior end of Spathidium is homologous 

 with the cytostome of such a form as Enchelyodon. In other 

 words, the mouth proper of Spathidium is really the depressed 

 area bounded by the slightly thickened edges of the anterior end of 

 the animal. It is always open and leads to the §lit-like cyto- 

 pharynx immediately below, the sides of which remain appressed 

 except when food is being ingested. This interpretation also 

 seems to be supported by the method by which food is engulfed, 

 which involves a grasping and 'mouthing' of the quarry by the 

 region bearing the trichites. 



Contractile vacuole. The Spathidia of the cultures under con- 

 sideration characteristically possess one large contractile vacuole 

 situated at the posterior end of the cell, though under certain 

 undetermined conditions animals now and then appear with two 

 smaller, closely opposed contractile vacuoles in the same situation. 



