93 



tbis matter to the bottom we must not merely study cabinet specimens, 

 but make numerous observations and experiments upon the living crea- 

 tuies. It is a big task and will need nianj^ workers, but it is well 

 worth the doing, both from the scientific and economic points of view. 



The situation is simply this: There is a prevalent tendency for dom- 

 inant tj^pes of Coccidie to become nuiltivorous orpolypliagic, and when 

 they have become so to any extent they are nearly always of serious 

 economic importance. But there is the reverse tendency for polyjdiagic 

 species to split up into monophagic races, varieties, and ultimately 

 sjiecies. As they do so their economic importance usually decreases, 

 and when it does not they are at any rate more easily dealt with. It 

 is for us to ascertain in each case by close observation how far these 

 processes of evolution have gone, and until we do so we can not rightly 

 understand the situation before us.* 



I can not refrain at this point from remarking on the utter inad- 

 equacy of the old-fashioned study of ^'iLiood species'* only, accompanied 

 by a vast contempt for all species or otherwise which were not ^'good." 



The new entomology will have to consider with equal care all phases 

 of insect evolution, from the individual, through the mutation, form, 

 variety, to species, good, bad. and indifferent. The old plan was 

 excellent for collectors of insects, but for economic entomologists, at 

 any rate, it Avill no longer do. In Coccidse x:)erhaps this is more obvious 

 than in any other grouii. 



Another notion that I think we shall have to give up is that these 

 evolutional processes all take ''ages.'' On the contrary, quite a number 

 of cases are now on record in which the habits and even the structure 

 of wild animals have changed within a few years. I need only remind 

 you of the Porto Santo rabbits, the Virginia Helix nemoralis, and the 

 Amphidasys betidaria var. douhledayaria in England to show that char- 

 acters which might be deemed specitic have begun to appear within a 

 few years under changed conditions of life. How many changes in 

 habit only have occurred we may never know, for it is only in striking 

 cases that they get recorded. But the whole literature of Coccidie teems 

 with records of species infesting in new localities plants they had never 

 before attacked. In many instances, as, for example, that of Orthezia 

 in.signis. we can not tell what were the original food plants. 



Among Coccid;e the rate of multiplication is prodigious, often prob- 

 ably more than a thousandfold in one generation, and the destruction 

 correspondingly great, giving full play to certain kinds of natural selec- 

 tion — i. e., those which ail'ect the ••staying power" of the individuals. 

 Among the many larv;e blown bj' the wind or carried by birds or insects 

 and among the many falling victims to parasites it may be largely a 

 matter of chance which shall survive. That is to say, the survival is 

 not necessarily due to any peculiarity in tlie individual. But those 

 which can live on an unwonted plant or can staiul adverse condi- 

 tions of weather survive by reason of inherent (pialities in themselves. 



*For a discussion of tbe tlieoretical considerations see Insect Life, vol. v, p. 117. 



