A REVIEW WITH HYPOTHETICAL CONCLUSIONS. 97 



migratory movements unnecessary, except on rare occasions, which may well be, 

 since by the terms of the definition they need only be undertaken when demanded 

 for the good of the species, and in response to unusual stimuli. These stimuli may 

 be, and frequently are, a direct result of a tendency toward overpopulation of the 

 locality from which the migrations are made. 



If the theory be well grounded, then, under exceptional circumstances, if not 

 habitually, Glossina ought to execute movements of quite a different character 

 from those incited by the ordinary needs of the individual, which is immediately 

 suggestive of the direct question, Does it do so ? There is nothing recorded of 

 its migratory movements to warrant an affirmative answer. The freedom with 

 which the flies move about within an infested area, as demonstrated by 

 Bagshawe, may be sufficient to provide for the seasonal movement noted by 

 Roubaud and others, and for the more extended movements recorded of 

 G. morsitans by so many independent observers. 



On the other hand, the bionomics of Glossina are not yet very well understood, 

 as is well exemplified by the lack of concise and satisfactory explanation for 

 certain frequently observed phenomena already mentioned. It is certain, when 

 the proper explanation of these phenomena is obtained, that they will be found 

 to be intimately associated with the protection or the alimentation of the individual, 

 or with the reproduction or dispersion of the species, and they are as likely to be 

 associated with dispersion — including migration — as with anything else. That is 

 to say, since our knowledge is surely lacking in some respects, it is quite as likely 

 to be lacking in respect to the migratory movements of the flies as in any other. 

 The writer himself believes that a connection between the phenomenon of sex 

 disparity and specialised migratory movements is capable of logical support, as 

 he will attempt to show in the following pages. 



Local Sex Disparity of Glossina Palpalis. 



It is well known that there is very often a marked disparity in the proportions 

 of the sexes of Glossina caught in one particular locality. This is best estab- 

 lished in the case of G palpalis, though it appears to be a common characteristic 

 of the genus, and various suggestions have been made as to the probable explana- 

 tion. That so many have been put forward is in itself sufficient to indicate the 

 unsatisfactory character of most of them. 



It is, in the case of G. palpalis, possible to associate sex segregation with 

 certain types of localities. This is not possible with G. morsitans on the basis of: 

 data at hand, nor of any other species so well as of palpalis. Some striking 

 figures are available. 



Kinghorn and Montgomery* made the following catches on the island of 

 Matondwi near the southern shore of Tanganyika : — 



In July, rf 1282, Q 127 ; 6 91 %, Q 9 % 



In November, <J 396, Q 5 ; 6 98'8 %,Q 1*2 % 



The island is small and uninhabited, but frequented by birds, crocodiles, somo 

 snakes and a species of mouse. It is two or three miles from the shore. 



* Annals ot Trop. Medicine, iii, October 1909, pp. 259-276. 

 31343 A 2 



