GLOSSINA OR SITUTUNGA ? 61 



Each without the other is harmless, for the Trypanosome 

 cannot multiply indefinitely in the fly, and requires to 

 live for a cycle in mammalian blood. 



Can the Situtunga be exterminated ? This would 

 be an extraordinarily difficult matter. It might be de- 

 stroyed, temporarily, on the islands, for there are very 

 iew localities where it would be out of reach. But on 

 the mainland there are vast areas of papyrus swamps 

 in which it finds sure refuge and where it would be quite 

 beyond reach. Now it is well known that the antelope 

 swims readily, and I have given an example of its wander- 

 ings on to islands where in the old days it was kept down 

 by natives. Hence it would easily swim out again to 

 the islands from the mainland papyrus swamps, and from 

 one part of the mainland to the other. If, however, a 

 price were put upon its head and natives were allowed 

 to destroy it, it might conceivably be kept to the papyrus 

 swamps, where, beyond the reach of Glossina, which is 

 never found in such localities, it would be harmless. 



As to the other side of the question, whether Glossina 

 can be destroyed, or at least so diminished in numbers 

 as to be harmless, there is a good deal to be said. It must 

 be remembered that when the fly is only present in small 

 numbers the chances of any one being infective are minute. 

 For every fly does not feed from a buck, and every buck 

 that is fed upon does not contain Trypanosomes. More- 

 over, as Miss Robertson has shown, if the buck does 

 contain Trypanosomes they are not always in a condition 

 ready to multiply in the fly when it bites, and lastly, 

 every fly that takes in Trypanosomes is apparently not a 

 suitable medium for their further development. 



When an undesirable insect is to be destroyed, it is 

 often found that the larval stage is easy to deal with, or 

 the next stage, when the insect is a quiet pupa or 

 chrysalis. 



But since there is no free larval stage in Glossina, 



