﻿Try panosome found in Pontobdella. 99 



The figures, which have had to be restricted from con- 

 siderations of expense in reproduction, hardly do justice to 

 the polymorphism of the trypanosomes (Figs. 14-27). 



Division. 



Division occurs with greater or less activity in every 

 stage of the life-cycle. The only form in which this process 

 has not been observed is the thread-like individual found in 

 the proboscis of the leech. It is in the early Herpetomonas 

 condition, however, that division is most frequent, and it is 

 in these forms that the nuclear detail has been most clearly 

 made out. The type of division here to be observed is a 

 primitive kind of mitosis. 



In the Herpetomonas stage before division, the nucleus, 

 as a general rule, presents eight well-defined chromosomes, 

 joined at their outer edges by the nuclear " membrane " or 

 outer chromatic ring, which is particularly distinct at this 

 stage (Figs. 4 and 11). The central karyosome is in the 

 shape of a fairly large ring, usually enclosing a blue staining 

 space. Occasionally a tiny granule may be seen in the 

 centre of the ring, but this is a rather rare and inconstant 

 feature; occasionally, also, the ring-shaped karyosome may 

 bear thickenings. In the very earliest stages the nuclear 

 pictures are a little obscure, but the following points are to 

 be made out. The nuclear " membrane " does not break 

 down at the beginning of mitosis ; the whole nucleus, 

 however, becomes slightly flattened into an oval, whose long 

 axis is at right angles to the axis of the first part of division. 

 The karyosome also becomes oval in the same direction, and 

 increases in size, although it usually becomes less definite. 

 Presently it is seen (Fig. 43) to have split longitudinally into 

 two irregular bands, or more often into two series of little 

 masses, whose outline is not by any means always quite 

 clearly defined. Between these two sets there stretches a 

 series of fibres which are, at first, a little irregular and 

 rather thick. As the nuclear membrane has, as a general 

 rule, not yet become much disturbed, the nucleus presents 

 an oddly double appearance (Fig. 43). 



