10 BULLETIN 120, UNITED STATES NATIONAL MUSEUM. 



a more or less transient fusion of alveoles along the axis of the body. 

 It is usually well developed and large in individuals that have been 

 kept for a considerable time in salt solution or Locke's solution out- 

 side the body of the host. It is probably as simple in structure as any 

 excretory organ known among the Ciliata. 



Within the posterior enlargement, " bladder," of the excretory 

 tube, one often' sees numerous small granules exactly resembling the 

 cytomicrosomes of the endosarc and ectosarc (fig. 28, 6), except that 

 the granules within the bladder stain somewhat differently. With 

 Delafield's hematoxylin they stain a dirty, dull, dark blue instead of 

 the clearer blue shown by the cytomicrosomes. These granules are 

 more abundant usually in the bladders of individuals kept for a time 

 outside the host, but they are often present in freshly taken indi- 

 viduals. 



One often finds individuals which have the posterior cilia, be- 

 hind the excretory pore, entangled in a mass of debris which drags 

 after the animal as it swims. In material freshly taken from the 

 rectum of the host one finds only a few individuals dragging such 

 debris after them, but in cultures kept for some time outside the 

 host most of the individuals will show such masses of debris upon 

 the posterior cilia. Though I have studied many thousands of living 

 individuals, keeping them under protracted observation, I have 

 seen only half a dozen times or so the actual expulsion of the gran- 

 ular mass from the excretory pore, but in some of these cases the 

 picture was very clear. It seems, therefore, that there is no regular 

 pulsation of the excretory bladder, but that there is an occasional 

 contraction with expulsion of the bladder contents through the excre- 

 tory pore. The excreta seem to be somewhat sticky and so to be- 

 come entangled in the posterior cilia. The extrusion of the liquid 

 contents of the bladder one would naturally regard as probably 

 equivalent to the extrusion of liquid from the excretory vacuole of 

 ParaTneciuTn or any of the higher Ciliates. But the interpretation 

 of the granules is more doubtful. They seem to be cytomicrosomes 

 which are cast off, but there seem to be no data to help us judge 

 whether the casting off of these cytomicrosomes is a part of the true 

 process of excretion. The role that they play does not seem to be 

 indicated. This association of cytomicrosome granules \vith an 

 excretory vacuole is not a unique phenomenon. In Amoeba froteus 

 there is a concentration of cytomicrosomes in the mass of protoplasm 

 which carries the excretory vacuole {See Metcalf (1910)), but only 

 in the Opalinidae, so far as I know, do such granules find their way 

 into the interior of the vacuole and then pass out of the body when 

 the excreta are expelled. 



