1911.]| | Trypanosoma gambiense 7m Glossina palpalis. 517 
In our experience, the long narrow forms, described by some observers as 
“male” forms, are exceedingly rare, and it seems impossible to ascribe to 
to them any very important dle in the process of development. Crithidia- 
like forms are also exceedingly rare—that is, forms with the micronucleus 
close to or anterior to the nucleus. 
Types of Trypanosoma gambiense found in the Salivary Glands.—On 
referring to Table I it will be seen that trypanosomes did not appear in these 
glands until the twenty-fifth day, but that after this time they were usually 
present. In our opinion, this invasion of the salivary glands is of the greatest 
importance in the history of the development of Trypanosoma gambiense in 
Glossina palpalis. Here it may be parenthetically remarked that, because 
one kind of development takes place with one species of trypanosome and 
one species of tsetse fly, it by no means follows that the same thing will 
occur either with another species of trypanosome or another species of fly. 
Each combination must be worked out separately and nothing left to analogy. 
Trypanosoma vivax and Glossina palpalis afford a striking example of this. 
In the development of Zrypanosoma gambiense in Glossina palpalis one 
cirtumstance, which we think of prime importance, emerges, and that is, that 
in the salivary glands, and here alone, the trypanosomes are found to revert 
to the normal blood-type. It must not be imagined, however, that the 
salivary glands show no other forms but this blood-type. On the contrary, 
there. are many other forms seen; but here only are found trypanosomes 
apparently identical with the short and stumpy forms tound in the blood. 
What causes or leads up to this reversion to the blood-type in the salivary 
glands is quite unknown, but, as will be seen later, the Glossina palpalis does 
not become infective by biting until this invasion of the salivary glands 
takes place. 
~ How the trypanosomes find their way into the salivary glands is also quite 
unknown. It seems highly improbable that they pass from the alimentary 
canal by way of the salivary duct, and as they are never found in the body- 
cavity, it is also difficult to see how they can make their way directly from 
the intestine to the abdominal portion of the salivary glands. 
