4«5 



From the foregoing it will be seen that, although in this 

 discussioh I have been obliged to take a critical attitude towards 

 the Simnlinm theory of this disease, our Illinois data are not. 

 by themselves, plainly conclusive either for or against that hypo- 

 thesis. This is a source of regret to me, although scarcely a 

 disappointment, as one entomologist, working for so short a 

 time and in so limited an area, could not expect to bring this 

 time-worn and complicated problem to the point of actual 

 solution ; and I must be content with bringing forward my 

 personal contribution of matters of fact to this important inquiry, 

 of a kind to reijuire that they be taken into account in forming 

 an adequate theory of this disease. In the meantime, whether 

 the Simulium theory be linallv justified or not, it should be 

 welcome to us, as 1 intimated in the beginning, as giving us 

 motive and opportunity greatly to increase our knowledge of these 

 interesting insects ; and it is particularly for this reason that I 

 have ventured to bring this imperfect discussion of a problem yet 

 nnsoh'ed before this congress of the entomologists of the world. 



