668 H. M. WOODCOCK. 



attenuation only in the fully grown forms. An intermediate 

 condition is seen in figs. 21) and oO. It will be noticed that 

 there is often considerable variation in the size of the nuclei 

 in these young or intermediate-sized individuals (cf. figs. 29— 

 33), even where the parasites appear very similar in size and 

 form. 'J'his feature is met with also in other series of forms 

 to be described (see below, p. 672). I do not think much 

 stress need be laid on apparent differences in size of these 

 organellee in comparing parasites otherwise similar. 



Unfortunately, as already mentioned, I could not obtain 

 any stained specimens of the parasite in the blood of the red- 

 poll during that period, owing to its scarcity, although I 

 had obtained cultures on two or three occasions. It was 

 early autumn before I could obtain series of permanent 

 preparations showing the trypanosomes in this bird ; and in 

 these smears, parasites which belong to the type above 

 described are relatively scarce and outnumbered by another 

 type. I have not found in this host at this period any 

 ordinary forms which have attained quite the dimensions of 

 the fully grown individuals occurring in the chaffinch in 

 the early part of the year. The individuals observed, how- 

 ever, correspond closely to the slightly smaller forms of the 

 parasite, which have been described above (cf., for instance, 

 figs. 33 with fig. 4, and, again, fig. 32 with fig. 31). Hence 

 I have little doubt that they represent that phase of the same 

 species, bearing in mind also the other considerations stated 

 already. It is probable that if I could have obtained examples 

 of the trypanosome in the blood of the redpoll in the early 

 part of the year I should have found " adult " definitive 

 forms similar to those in the chaffinch. 



The predominating form of the trypanosome in the blood of 

 the redpoll in the autumn (September, and again in October), 

 is a very large parasite. Some of the individuals of this new 

 type are, in all respects, the largest trypanosomes I have 

 observed in the birds, being not only as long as the longest 

 ordinary individuals, but also much stouter. The individual 

 drawn in fig. 37, for example, measures 48 f.i in total length 



