678 II. M. WOODCOCK. 



schizogony, I tliink it is not at all unlikely that naturally 

 occurring trypanosomes — about whose life-cycle in the Verte- 

 brate host very little is yet really known — 1x1:13' show some 

 such schizogonic process more commonly than has hitherto 

 been supposed.^ In default of such a pi-ocess in the present 

 case, I have no idea how the small forms are developed, since 

 they certainly do not appear to be derived from the adult 

 ordinary individuals. 



Another question is, What becomes of the ordinary, definitive 

 forms of the trypanosome ? As I have obtained many suc- 

 cessful cultures from birds where this was the only type 

 present in the blood, the natural inference would be that 

 this form can be transmitted to the insectan host ; but the 

 same applies equally, it must be noted, to the fusiform 

 parasites of case B, since I obtained cultures from them also. 

 And I cannot be certain that both these types would develop 

 naturally in the insect. Some of the ordinary forms, later 

 on in the season, may pass into the large, massive type ; this 

 is not at all unlikely, if the latter is really a multiplicative 

 form. The individual di-awn, for instance, in fig. 39 may 

 perhaps represent an intermediate stage in such a transition. 

 Another possibility, of course, is that this definitive type 

 disappears altogether in the summer, its place being taken 

 by the fusiform type; the condition of the infection would then 

 correspond with that of case B. I do not think this is likely. 

 Case B most probably represented a recent infection (see 

 below) ; in such the condition may quite likely differ from that 

 found in an old established infection. Moreover, in the earlier 

 case A (about the middle of March), parasites of the ordinary 

 type are quite numerous, and do not look like disappearing; 

 and further, in the autumn, in the redpoll, this type is also 

 present. 



It remains for me to say a few words with regard to the origin 



> A most interesting piece of evidence hearing iipon this point is 

 supplied by Minchin (12). who mentions and figures the occiirrence of 

 a large individual of T. perea?. which is apparently in an encysted 

 condition. Such a form might very well l^e about to undergo schiz ogony . 



