2 3 o THE HAEMO FLAGELLATES 



taking place in the leech, after various regulatory or matura- 

 tion processes have been undergone. The copulae give rise to 

 the three general types, distinguished principally by nuclear 

 differences. 



In the case of T. lewisi, Prowazek states that soon after reaching 

 the mid-gut of the louse, the parasites undergo reduction of the 

 nuclear apparatus, by which the number of chromosomes is said 

 to be reduced from sixteen to four. The gametocytes (parent- 

 individuals of the gametes) are not strikingly differentiated from 

 one another, but in the formation of the microgamete from the 

 male form, the body becomes diminished in size, its nucleus 

 (trophonucleus) very elongated and at first spirally twisted, then 

 band-like, while also the cytoplasm stains differently from that of 

 the female element (megagamete). 



Coming now to what is known of the development of Mam- 

 malian Trypanosomes in Tsetse -flies (Glossinae), we have first to 

 mention the knowledge obtained by Minchin, Gray, and Tulloch (59) 

 with regard to T. gambiense in G. palpalis. This, unfortunately, is 

 largely of a negative character, owing in all probability (as we have 

 seen earlier) to this species of fly not being the correct alternate 

 host, but one in which the attempts of the parasite to continue its 

 life-history are, for some reason, unsuccessful. Nevertheless, the 

 important observation that the types already recognised as male 

 and female in the blood of the Vertebrate at first greatly pre- 

 dominate, with, moreover, a much more marked differentiation 

 of sexual characters and without any forms intermediate in 

 type, is also strongly in favour of *,he idea that conjugation 

 occurs, in general, soon after the arrival of the Trypanosomes in 

 the insect. 



No mention is made by Stuhlmann (80), in his highly interest- 

 ing account of T. brucii in G. fusca, of the occurrence of any similar 

 phases, or of anything in the nature of ookinetes, at the beginning 

 of the infection. The first individuals found by this investigator 

 were of the indifferent type, occurring in large numbers in the 

 hinder part of the gut, two to four days after infection of the fly. 

 It seems probable, however, that Sttfhlmann missed some early 

 essential phases of the development, since, as said above, Leger 

 found ookinetes of T. barbatulae eighteen hours after feeding, while 

 Minchin and his collaborators say that the sexual forms were best 

 developed after about twenty-four hours, while by the end of forty- 

 eight hours a type of more indifferent character was making its 

 appearance. According to Stuhlmann, the indifferent parasites 

 apparently spread forwards through the mid-gut, but usually pass 

 right forward only when the flies are fed again (from an uninfected 

 animal). By this means the presence of the Trypanosomes in the 

 proventriculus was obtained, and in the " long " form, quite similar 



