218 E. A. MINCHIN. 
in the digestive tract of the fly are developmental, and not 
merely multiplicative forms, and are not ripe, so to speak, 
for transference to the vertebrate host. Novy (82) considers 
this to be due to T. gambiense having died out in the 
flies, but this is certainly not so in our experiment (pp. 227, 
234), in which case the fly’s intestine contained numerous 
active ‘I’. gambiense. In the latter paper of Novy, Mac- 
Neal and Torrey (p. 262) it is stated that “the fact that 
ingested trypanosomes lose their virulence so rapidly in the 
stomachs of insects indicates a loss of functional activity, 
especially of the power of multiplication.” This, again, is 
certainly not the case; multiplication of the trypanosomes 
proceeds continually in the gut of the insect. | 
In my opinion the evidence now accumulated (I may 
mention especially Brumpt [10] and Prowazek [86] in 
addition to the authorities already cited) is conclusive in 
favour both of the general statement, that trypanosomes 
undergo development, as distinct from multiplication, in 
invertebrate hosts, and of the more special proposition, that 
certain species do so in tsetse-flies. I wish now to offer a 
few suggestions upon the mode of their development and the 
nature of the invertebrate cycle, as it may be termed. The 
possibilities of trypanosome development are bound up with 
the question of their possible or probable phylogeny and 
course of evolution in the past.' 
Many authorities have pointed out that trypanosomes 
may possibly, if not certainly, have two distinct ancestral 
origins. The firstis from a Trypanoplasma-like ancestor 
in which the anterior flagellum has been lost; this is the 
“trypanosome with flagellum morphologically posterior” 
1 As I pointed out in the discussion on Heemoflagellates before the British 
Medical Association at Exeter, where I have ventilated some of the views 
here expressed. My phylogenetic speculations were, however, put aside by 
Sir Patrick Manson, who expressed the view that where a parasite is now 
found in two hosts, for instance, a vertebrate and an arthropod, it was inherited 
by both of its hosts from their common ancestor (see ‘ Lancet,’ September 7th, 
