﻿150 JAS. J. SIMPSON— ENTOMOLOGICAL 



In Table B are given the monthly records of the rainfall for 22 stations 

 throughout the Colony for the years 1909 and 1910. These have been arranged 

 in order of descending totals for the year 1909, and while it will be noticed that 

 for this particular year the order is not precisely the same as in the table of the 

 mean annual rainfall for the six years, still the grouping is not materially 

 affected. A comparison of the tables for 1909 and 1910 also shows that there 

 are certain discrepancies, and that although there is, in general, a diminution from 

 the south northwards, certain stations, for example, Ondo and Olokemeji, do not 

 fall within this category. The reason for this is not at first very evident, but an 

 examination of the tables will show that in the drier regions where there are 

 large hills or dense forest, the rainfall is always greater ; this explains away the 

 apparent anomaly of Ondo, Olokemeji, and stations in the vicinity of the 

 Kameruns. 



Let us now consider for a moment the duration of the dry season in the various 

 regions, and for this purpose we may neglect a rainfall of below To inches in any 

 one month. In 1909, at no station were there two months without any rain, 

 while, even disregarding 1*5 inches, never did the number of dry months exceed 

 three. The driest months were December and January ; February came next 

 with a low rainfall, and only slightly higher was November. In 1910, however, 

 November, December, January and February might be regarded as compara- 

 tively dry months, but it will be seen that in the delta region at Akassa and 

 Brass even in February there was a rainfall of 5*49 inches and i'57 inches 

 respectively, while in November the rainfall at Brass, Bonny, and Akassa was 

 12*52, 11*52 and 6*77 inches respectively. 



Generally speaking, the dry season lasts from November to February and 

 tends to increase in length from the south northwards. This will be most easily 

 seen by comparing Calabar, Bonny, Brass and Akassa with Olokemeji, Oshogbo, 

 Otta and Ibadan, but even then one must always bear in mind that in different 

 years rain may fall during all four months. Consequently, it is hardly justifiable 

 to speak of a true dry season in Southern Nigeria. In the inland parts there is 

 an approach to a dry season, and this period gradually increases in Northern 

 Nigeria, until in the northern regions of that Protectorate there is a definite 

 division of the year into a wet and a dry season. 



The records of blood-sucking insects from both Northern and Southern Nigeria 

 are perhaps too scanty to admit of any definite deductions being drawn, but in 

 another part of this paper, when discussing the genus Glossinu, I hope to show 

 that the distribution of the various species in these two colonies is closely corre- 

 lated with the rainfall and relative humidity. 



A consideration of the monthly rainfall at Ondo and Olokemeji will show how 

 the apparent discrepancy in the total rainfall for the year is brought about. 

 Although the annual total is greater in this region than one would be led to 

 expect, it will be seen that this is due, not to a rainfall extending over a greater 

 number of months, but to a greater monthly intensity during the rainy season. 



A comparison of the monthly records for the various stations in Table B will 

 also show what is meant by two annual maxima. It will be evident that, as a 

 general rule, although it varies in different years and at various stations in the 

 same year, the rainfall increases gradually from January to about the end of 



