200 E. A. MINGHIN. 
observations extend, get further forward than the hinder 
part of the intestine. It would be interesting to know if the 
slender forms penetrate as far as the proventriculus. Unfor- 
tunately none of the flies examined by me had trypanosomes 
in the proventriculus. 
The slender form and the H-form are in all probability to 
be regarded as propagative forms, that is to say, as forms 
destined to spread the species to other hosts. In favour of 
this view may be urged their small size and great activity, the 
absence of multiplication amongst them, their mode of 
occurrence in the fly, and their constant structure, far 
removed from that of the ordinary blood-trypanosome and 
more approaching the Herpetomonas or Crithidia type 
of structure, that is to say, the type of structure usually 
associated, in these organisms, with parasitism in the gut of 
insects. ‘lhe H-form becomes encysted iu the proctodeum, 
and the cysts are doubtless destined to pass out with the 
feeces. What is the destiny of the slender type? ‘The 
manner in which it extends forwards in the gut suggests 
strongly that it may be destined to infect fresh hosts by the 
inoculative method. 
To sum up my conclusions as to the various forms of Try - 
panosoma grayi: They may be subdivided at the outset 
(using Doflein’s appropriate terms) into (1) multiplicative 
forms, varying greatly in size and structure ; and (2) propaga-_ 
tive forms, very constant in both respects, but of two types. 
One of the propagative types terminates its lodgment in the 
fly by becoming encysted in the hind gut; the other is 
perhaps destined to pass forwards through the proboscis. 
If the two types hitherto regarded as male and female be 
not in reality such, the question arises whether any of the 
numerous forms of T. grayi are to be regarded as sexual. 
It is usual, when slender and stout forms of trypanosomes 
occur together, to interpret them as male and female; but the 
only final and conclusive proof of such forms being sexual in 
nature is to find them conjugating. I have spent much time 
trying to find stages of conjugation in my slides of T. grayi, 
