﻿Trypanosome found in Pontobdella. 87 



present the little resistent creatures in the rounded off or 

 very early Herpetomonas stage ; these may sometimes be 

 quite minute, and seem to be able to persist through a period 

 of starvation, and may preserve the infection without any 

 external aid (Figs. 60-62). Thus in a freshly captured leech 

 which showed the blood in the crop in a perfectly unaltered 

 condition, and in which I could find no parasites of the T. raice 

 type, there were a large number of these very minute rounded- 

 off forms, and also the regular cycle of derivatives, i.e., the 

 Herpetomonas and trypanosome stages all in miniature, and 

 showing signs of division. These forms proceed to grow, and 

 may sometimes rather confuse the infection. Thus you may 

 apparently get a persistent infection and a fresh one at the 

 same time. 



The long forms appear to degenerate and die if they remain 

 in the leech, and this, in correlation with the presence of 

 trypanosomes in the proboscis, suggests very strongly that this 

 parasite is a digenetic form — the skate being, of course, the 

 most likely vertebrate host. Still the late work of Professor 

 Minchin and others shows how carefully this point must be 

 gone into before one may conclude that similar flagellates 

 occurring in a vertebrate and a blood- sucking parasite belong 

 to the same cycle. 



I propose to begin the description of the various stages of 

 this trypanosome with the rounded-off form (Figs. 3, 5-8, and 

 10) possessing no locomotor apparatus. In this condition the 

 parasite is a roughly circular organism with a conspicuous 

 trophonucleus and a relatively large kinetonucleus. 



The protoplasm of this form, which is found in the intestine 

 and also at times in the crop, presents few features of interest ; 

 it is finely alveolar, and vacuoles are sometimes present, so 

 also are granules. 



The trophonucleus is typically composed of eight chromo- 

 somes arranged in a circle round a central karyosome. The 

 chromosomes may be connected to the karyosome by fine rays 

 (Figs. 3, 6, 10). While this arrangement is often diagram- 

 matically clear, nevertheless great variations may occur. The 

 chromosomes may be obscured, the nucleus may assume a 

 reticulate character (Fig. 5), the number even of the chromo- 



