species ot Tsetse, as also of their mode of reproduction and feeding, 

 their habitat, geographical distribution, the extension or contraction 

 of areas in which they are found, etc. A large number of specialists 

 entomologists, medical men and others are devoting their energies 

 to the problems presented by these insects, and data, published in 

 technical journals, continue to accumulate. But the greater the 

 progress in scientific knowledge of Tsetse-flies, the clearer it becomes 

 that what is already known amounts to little indeed in comparison 

 with what we have yet to learn, and we are confronted with many 

 questions, on the solution of which depends in some degree the economic 

 future of large regions of Tropical Africa. Thus we know but little 

 at present on the subject of the predacious enemies and parasites of 

 Tsetse-flies, although in undertaking a campaign against these formid- 

 able Diptera a knowledge of such enemies would be of importance. 



A profound study of the zones infested by the different species of 

 Tsetse at the various seasons of the year ; of the migrations and other 

 movements of these insects ; of the conditions governing their breeding ; 

 of the spots in which they deposit their larvae, etc., might likewise 

 suggest effective methods of destruction or limitation, by modifying 

 the environment of the flies, or by means of other prophylactic measures. 

 Lastly, a study of the various methods of capture and of the influence 

 of external agents heat, light, humidity, colours and odours might 

 also be expected to lead to results of practical value. 



The present little work has been written for the benefit of those who 

 desire to study Tsetse-flies in various parts of Tropical Africa, and,, 

 as has already been indicated, its object is simply to furnish them with 

 information as to the biological facts already ascertained and the 

 points that still require investigation. 



Since it may be that an apparently insignificant detail will provide 

 the solution so keenly looked forward to, our knowledge of Tsetse- 

 flies should be as exhaustive as possible, and everything pertaining to 

 these Diptera should be observed and noted down. Thus, collections 

 should be made of specimens of male and female flies, and of larvae 

 and pupae ; while investigators should record observations on habitats, 

 extension or contraction in limits of occurrence, method and time of 

 feeding, animals upon which the insects feed, influence of atmospheric 

 factors, local and general geographical distribution, copulation, 

 deposition of larvae, breeding-places, duration of the pupal stage, 

 proportion of the sexes, predacious enemies and parasites, diseases, etc. 



With regard to the apparent diffuseness of certain of the following 

 chapters, it should be explained that this is due to the fact that state- ' 

 ments by different observers, working in widely separated regions, 

 are often contradictory, and that, in order to be impartial, we have 

 felt it necessary to give a resume of the various opinions. The chapters 

 on the areas occupied by the different species of Tsetse, and on the 

 influence of big game, are cases in point. 



The attention of those desirous of making investigations in Belgian 

 Congo is specially directed to the question of the distribution of the 

 [various species of Glossina in the different regions of that vast terri- 

 tory. It is important that a map should be prepared without delay, 

 showing as accurately as possible the distribution of these insects in 

 Belgian Congo, since such a map would be of great assistance in 

 connection with the campaign against sleeping sickness and the 

 establishment of cattle-breeding centres. 



