270 H. LYNDHURST DUKE. 



dealt with by limited measures such as trapping, attention to possible remaining 

 breeding grounds, etc. 



After a temporary rise in level, subsequent falling of the lake will, of course, lead 

 to exposure of the breeding area in a particularly favourable state. The progeny 

 of the fly that survive, if left alone, will in course of time re-establish themselves. 

 To ensure success, therefore, with a temporary raising of the lake level, the islands 

 and shore line that it is especially desired to reclaim must first be carefully studied 

 with a view to the proper organisation of coincident clearing of potential breeding 

 grounds. A permanent rise in level will, I think, have a more serious effect on the 

 fly and some time will elapse before new breeding grounds can be found at the new 

 level. 



There is only one known outlet to Lake Victoria, namely at the Ripon Falls, Jinja. 

 The Falls are about 300 yards wide, divided into 3 parts by two islets. If a 

 permanent dam were erected at this spot the level of the lake could be raised. 

 Further, such a dam would prevent the falling of the lake, which sooner or later 

 follows high levels such as those of 1906 and 1917. 



I have discussed the construction of such a dam with Mr. C. V. Espeut, the 

 Director of Public Works, Uganda, who tells me that the undertaking is quite feasible. 

 He is, however, unable without careful consideration to estimate the [cost of the 

 structure. 



Considerable time, possibly 12 months, would jelapse after the erection of the dam 

 before the lake level became once again constant. 



If the contentions advanced in this paper be [correct, the result of the dam will 

 be either the practical extermination of the fly on Victoria Nyanza, or so marked 

 a reduction in their numbers that survivors will be easily controlled. 



Confirmation of my observations will, I fear, be difficult. Capt. Carpenter, who 

 has for years studied G. palpalis in Uganda, is still detained on active service. The 

 lake level is dropping steadily and the fly are in consequence doubtless once again 

 increasing in numbers ; and it is highly probable that before very long the fly 

 popultion may reaach its former density. But the results of this 1917 rise of the 

 lake appear to be in perfect accord with the deductions made by Fiske as a result 

 of months of careful study in 1912-13. 



References. 



(1) G. D. H. Carpenter, Reports S.S. Commission of Roy. Socy. XII. j 



(2) W. F. Fiske, Progress Report XIV. 



