THE HAEMOFLAGELLATES 231 



to the type occurring in the proventriculus and oesophagus of freshly 

 caught " wild " flies. 



This type manifestly corresponds to Miss Robertson's very 

 slender forms in the front part of the gut and proboscis of the 

 leech ; the agreement extends to the ladder-like arrangement of the 

 chromatin (chromosomes 1) of the trophonucleus. Whereas, how- 

 ever, in T. raiae, it is these forms, or their derivatives, which appear 

 destined to return to the fish, Stuhlmann found, in the proboscis 

 of freshly caught Tsetses, little Crithidial forms (" small " forms), 

 with the kinetonucleus alongside, or on the flagellar side of the 

 trophonucleus. 1 Stuhlmann regards these individuals, which he was 

 unable to obtain in artificially infected flies, as representing the 

 phase in which T. brucii is transmitted to the Vertebrate ; though 

 he states that the long forms seem to degenerate in the pro- 

 ventriculus after a time (as well as the small ones). In no case, 

 unfortunately, was he able to actually infect a Vertebrate by means 

 of either kind, which suggests that there is some other, as yet 

 unknown, factor or condition concerned in this perplexing question. 



Stuhlmann describes and figures certain phases found in one case 

 in the proventriculus of an artificially infected fly, which he thinks 

 are perhaps indicative of conjugation. In all the stages figured, 

 the cytoplasmic body of the parasite is single; the nuclear and 

 locomotor organellae, on the other hand, show different conditions 

 from single to double. Of course, here as in so many other cases, 

 it is entirely a matter of the sequence in which the figures should 

 be taken. Stuhlmann's chief reason for his interpretation is that, 

 in what he regards as the earlier stages of union, the flagella lie on 

 opposite sides of the body ; whereas, in the usual mode of division, 

 the two flagella lie on the same side of the body. Still, Stuhlmann 

 himself agrees that the condition may be only one of an unusual 

 mode of division ; and this seems the more likely explanation, for 

 such a mode of division has been observed in T. leivisi. 2 



That the course of a Trypanosome life-cycle may take, however, a. 

 quite different direction from that outlined in the above instances is 

 proved unmistakably by Minchin's valuable investigations on Trypano- 

 soma grai/i (57 and 58), which led him to the unexpected discovery 

 of the encystment of this form in the proctodaeum of G. palpalis. 



Minchin recognises three well-marked types of this Trypanosome 

 in the fly. (a) The ordinary type, having a multiplicative function, 

 and probably giving rise to the swarm of parasites often found. It 

 is usually of large size, and shows great variability, especially in 

 the position of the kinetonucleus. While generally a little in front 

 (i.e. on the flagellar side) of the trophonucleus, it may be alongside, 



1 For an account of the proboscis - forms recently described by Roubaud, see 

 Postscript, p. 261. 2 Cf. footnote, p. 225. 



