No. 3-] BIOLOGY OF THE STENTORS. 545 



region indicated by Claparede and Lachmann ('59), Stein ('67), 

 and Moxon ('69) — on the dorsal side at the same level with, 

 and a little to the right of, the contractile vacuole. (Fig. 63, a) 

 But the evacuation of excreta is by no means always at this 

 place ; sometimes they are extruded at a spot but slightly re- 

 moved; sometimes at places far distant, as at the lower part of 

 the dorsal region, or on the right and left sides of the animal 

 (Fig. 63, fc). These observations have been made upon 

 animals not under cover-glass pressure, but living under free 

 conditions. It cannot, therefore, be supposed, as Butschli 

 ('89, p. 1386) has done in case of a similar observation by 

 Brauer upon Biirsaria truncatella, that the evacuation of 

 excreta in places other than the usual is due to pressure. But 

 a statement should be made regarding the character of the 

 substance discharged. It consisted in most instances of 

 minute green algae (in the example shown in Fig. 63, of 

 Scenedesmus), which vS". ccerulens sometimes devours in large 

 quantities, but to all appearances does not digest; for the algae 

 are discharged in as bright and green a condition as they are 

 taken in. Hence the evacuation of such ingesta is not the 

 same thing as the discharge of the residue of digestion. But 

 if undigested excreta can be extruded through the pellicula at 

 various points, can we venture to assert that faecal matter may 

 not also be eliminated at more than one place .-* 



Since in most Infusoria^ no morphological structure indicates 

 the place of the anus, why is defecation for the most part 

 confined to a particular region of the body .^ It is unquestion- 

 ably due to the fact that, after digestion is completed, faecal 

 matter is brought by the slow streaming movement of the 

 endoplasm to one particular place, and there accumulates until 

 the time of defecation. In ^. cceruleus a large excrement- 

 vacuole may be seen lying near the dorsal surface of the body, 

 about at the level of the contractile vesicle. I have seen two 

 excrement-vacuoles in this region come into contact and then 



1 Maupas {'83, p. 650) has expressed the view that the anus is permanently 

 present as a deft in the pellicula, which opens only at time of defecation. 

 Biitschli ('89, p. 1387) adopts this view, and even finds in Balantidium a perma- 

 nent anal pore. An anal tube was figured and described by Stein ('67) in 

 Nyctotherus. 



