﻿Trypanosome found in Pontobdella. 



85 



alterations. For instance, division which in most free 

 Protozoa occupies at most three to four hours, and is far 

 more often completed in less than one hour, may here be a 

 very slow process. Thus, on several occasions, individuals 

 in various stages of division were watched for periods of from 

 five to seven hours, only the slightest changes being seen. 

 The question naturally arises as to whether the conditions 

 under which the animals are observed may not account for 

 this retarding of the development. However, the extreme 

 slowness of the processes of digestion make it very probable 

 that succeeding stages follow each other more slowly than in 

 other forms. A striking feature in the development of this 

 trypanosome is the number of different stages that may some- 

 times be seen at one time in the leech. The observation of 

 these in the living state is most instructive, as the stages 

 are often bound together by the finest gradations. On one 

 slide, if the material is favourable, all the transitions may 

 be seen, from a stumpy, round organism with a short, thick, 

 and quite stiff flagellum, to a fully developed and even very 

 slender trypanosome. These stages are to be described later 

 on in this paper, and they are only mentioned here as they 

 form an interesting comment upon the present tendency 

 to classify the trypanosomes according to the relative posi- 

 tions of their kinetonucleus and trophonucleus. 



From the observations I have been able to make upon 

 freshly captured Pontoldella in various conditions, it appears 

 to me that the animal fills its crop at one meal, and then 

 proceeds slowly to digest the contents without seeking food 

 until all the blood is pretty well assimilated. 



It is convenient here, for the sake of clearness, to run 

 rapidly through the cycle of forms before describing them in 

 detail. In the crop and the intestine of newly or com- 

 paratively newly fed leeches there are found rounded off 

 organisms presenting both a trophonucleus and a kineto- 

 nucleus, but no locomotor apparatus (Fig. 3, Figs. 5-8, and Fig. 

 10). It is this form that Brumpt holds to be derived from 

 Trypanosoma raice. These individuals, which are usually 

 dividing fairly actively, gradually disappear entirely from 

 the crop, and are to be seen only in the intestine. This 



