﻿Trypanosome found in Pontobdella. 97 



sion of a much greater elasticity, some of tlie movements, as 

 I have stated, resembling those of the larger Spirochaetes, as 

 Sp. anodontce. Thus it may execute a figure 8 and other 

 complicated movements repeatedly while remaining on the 

 same spot. It may sometimes be seen with one end curled 

 up into a circle, or may even fold itself in two like a 

 penknife. 



At a later stage of the digestion, a still more slender, 

 practically thread-like form is developed, which agrees with 

 the last in all points except that it is smaller and much 

 more slender, and the trophonucleus has a tendency to lie 

 nearer to the kinetonucleus. It is this form which is found 

 in the proboscis (Figs. 26 and 27). 



The other main type is a relatively very broad organism, 

 with sometimes a relatively smaller kinetonucleus. The 

 flagellum is, however, usually fairly long. The tropho- 

 nucleus is often of the type which presents the large blue 

 staining karyosome with scattered red granules (Figs. 15-19). 



Typical nuclei with eight chromosomes and a small 

 karyosome are also met with, and in some specimens the 

 nucleus has a rather irregular and scattered appearance. 

 The protoplasm of this form stains deeply, sometimes with 

 a pinkish tinge. It moves fairly actively, but not very 

 rapidly through space. 



These forms, i.e., the long, slender trypanosomes and the 

 broad form just described, are joined up by a number of 

 intermediate stages (Figs. 20-24). 



One is naturally led to suspect a sexual differentiation in 

 these forms. I hesitate, however, to assert that the broad 

 individuals are female forms and the slim individuals male 

 forms, and that for several reasons. 



Firstly, I have never yet observed conjugation ; further, 

 although this difference in appearance is generally held to 

 indicate a sexual differentiation, there is in this trypanosome, 

 so far as my experience goes, no evidence that can be held 

 to directly support such an hypothesis. Moreover, the 

 number of intermediate stages, and the great variability 

 in size of the broad individuals, suggests the possibility of 

 this difference in appearance being a physiological question, 



VOL. XVII. H 



