IN THE ILORIN PROVINCE OF NORTHERN NIGERIA. 13 



a retreat for the flies, whence they spread over the surrounding country during 

 the rains. I therefore recommended that all the undergrowth should be cleared 

 away, and that the marsh itself should be drained by digging a ditch through 

 the middle. This was done, apparently with good results, for although the 

 haunt was thoroughly searched in July, August and September — that is during 

 the height of the rains — no tsetse-flies could be found ; and the European 

 residents informed me that they had not observed any in their offices or 

 bungalows. 



As already stated there are in the western division some isolated patches of 

 bush, skirting the smaller streams or surrounding pools, in which I was unable 

 to find tsetse-flies although the local conditions appeared to be suitable. This 

 fact suggests that, in the event of a patch of bush becoming isolated by 

 cultivation or otherwise, it remains for some time a tsetse-haunt, and as in the 

 case of the swamp at Offa, serves as a retreat for the flies in the dry season ; but 

 that eventually its tsetses die out, a process that may be accelerated by clearing 

 away all undergrowth. 



The Small Race of G-. palpalis found in Ilorin. 



By far the most common tsetse-fly in Ilorin is one which differs markedly in 

 external characters from any of the recognised species, but which has been 

 identified as G. -palpalis by both Professor Newstead and Mr. Austen. It is a 

 small fly, with abdominal markings practically identical with those of G. tachi- 

 noides, with the one exception that the buff colour of the paler areas is replaced 

 by a very characteristic grey-blue tint. Specimens were sent to the Entomo- 

 logical Research Committee, and were very kindly examined by Mr. Marshall, 

 who wrote saying that he could not regard them as being specifically distinct 

 from G. palpalis because the genitalia of the males" were practically inseparable. 

 In another letter he wrote that they constituted the principal difficulty in 

 dealing with my collections, for he had found discoloured specimens of G. tachi- 

 noides extremely hard to distinguish from this very small race of G. palpalis. 



* In a fresh preparation the details of the genitalia of the male differ considerably from those 

 seen after treatment with caustic potash. Maceration, as might be expected, destroys all the 

 finer structures, and distorts the natural arrangements of the organs. This is conspicuous in 

 the case of the inferior clasper. In a macerated specimen the terminal portion of the inferior 

 clasper is extended into a leg-like process, ending in a foot-like extremity which overlaps its 

 fellow of the opposite side in the middle line. In a fresh specimen, on the contrary, the leg-like 

 process of the inferior clasper is seen to be bent upwards into an S-shaped structure. The first 

 bend occurs at the proximal end of the process in an upward and outward direction, the 

 second in the middle of the foot-like extremity in such a way as to curve the toe upwards 

 and backwards over that part of the extension which, to preserve the analogy, must be called 

 the ankle. Looking at the hypopygium from above, therefore, in a specimen from which the 

 point of the superior clasper has been broken off on one side, a clear outline of the broad basal 

 portion only of the inferior clasper can be seen at the lowest focus. On raising the focus a 

 little the ankle of the leg-like process comes into view, with the sole of the heel and the folded 

 border of the toe forming a line parallel to, but behind, the lower incurving border of the 

 broad basal part of the clasper. At the highest focus only the toe is seen clearly, its tip 

 pointing directly backwards. In a side view the extension of the inferior clasper resembles a 

 snake poised with its head drawn back ready to strike. 



