D and E combined from 975 to 1,303. This latter result might 

 lead to gn increase of the number of predators in the area, or 

 to an increase of the more cryptic forms of the food of the pred- 

 ators, owing to a greater amonnt of a more easily procured food. 

 I do not imagine that this is the only method by which an 

 introduced species supplants an endemic form ; many complex 

 causes may lead to the same result. During a discussion on 

 this subject at a former meeting. Dr. Back stated the case of 

 two species of Aleyrodes in Florida attacking Citrus: Aley- 

 rodes citri and A. citiifolia. When citrifolia is present in 

 quantities in an orange grove and citri is introduced, the latter 

 soon supplants the former as a pest. In this case. Dr. Back 

 stated, there is no reason to consider that parasites, insect or 

 fungus, play any part, but that the ascendancy of citri over 

 citrifolia is due more to a slight diflference in fecundity and 

 life history. The elucidation of this, and similar problems, is 

 of great interest, and of value to bionomics as well as economics. 



Specific Characters axd Mortality of I:m mature 

 ixdividfals. 



One of the chief things that has been impressed upon me 

 during many years of observations of the death factors of in- 

 sects, is that the mortality is highest in the immature stages. 

 ISTatural Selection has but a limited field in the adult stage. 

 It would be easy to quote figures to show this, especially among 

 the Ilomoptera. Mr. J. C. Kershaw, after many years' study, 

 came to the same conclusion in regard to the Lepidoptera of 

 South China. This fact must be borne in mind when we con- 

 sider the origin of adult specific characters by Natural Selec- 

 tion. 



The vast majority of specific characters are such that we 

 cannot conceive of them being selected on account of their 

 utility and they have no connection with the earlier stages of 

 the insect. We have only to take up a Monograph of some one 

 large genus and note the characters which distinguish the spe- 

 cies from one another ; it is only by insisting upon our ignor- 

 ance that we can maintain our belief in their vital utility. Take 

 for instance our genus of Proterhinus ; he would be a bold man 

 who would try to maintain that each specific character was of 

 a life-and-death value to its possessor. Or take the genus Per- 

 h-insiella; here are some fourteen s]>ecies living on the same 



