86 THE SCOTTISH NATURALIST 



Any investigations, therefore, which aid us in controlling 

 the enormous numbers of these germ-carrying, food-destroy- 

 ing and herd-infesting pests, by throwing light upon the 

 various details of their life-histories and habits, and thereby 

 enabling us to attack them in their most vulnerable point, 

 must be regarded as of supreme importance. That such is 

 now realised to be the case is effectively shown by the great 

 increase in the literature of the subject during the past 

 twenty years or so. Especially is this so in regard to the 

 species concerned in the spread of disease. Before the epoch- 

 making discoveries of Major Ross, Drs Manson and Bruce, 

 and others, the number of published memoirs dealing 

 exclusively with Diptera was a comparatively small one, 

 but since our attention was thus directed to the subject the 

 percentage has increased to a notable extent. From the 

 pages oi the Zoological Record we may obtain some instructive 

 statistics. For instance, in the year 1885 some 375 titles are 

 given of papers and books devoted to insects, and of these 

 twenty-one are devoted entirely to Diptera, i.e., between 

 5 and 6 per cent. Ten years later the number of titles was 

 125 1, of which 112 refer exclusively to this Order of insects, 

 the percentage thus having risen to 9. In 1905 the titles 

 number 1669, the papers on Diptera 186, while the percentage 

 works out at 11. 14. Lastly, in the volume for 1913, the 

 latest accessible to me, the entomological titles amount to 

 2967, those referring to Diptera alone being 436 — a per- 

 centage of 1 1.32. Thus, in spite of the heavy increase in the 

 output of insect literature in general the percentage dealing 

 with Two-winged Flies seems to maintain a steady increase. 



From this rapid growth in the number of books and papers 

 on Diptera there arises a considerable disadvantage to the 

 student in one important respect. It becomes increasingly 

 difficult to cope with the contents of this continually 

 augmenting literature, and access to all the works written 

 on the subject is becoming every day a more and more 

 hopeless task. This state of things applies as much to the 

 study of British Flies as it does to the forms inhabiting 

 other countries. There is crying need for some work which 

 would bring together within a reasonable compass the great 



