AND DEVELOPHENT OF COMTS INFELlX, 237 



lizards, &e. It is a recognized method to reduce a pest by introducing some enemy 

 from another country. This has been done in America against injurious scales, l)y 

 introducing little Chalcid flies from Europe. 



Thus the basis of economic entomology is life-history work, which has wider bearings 

 than merely following and observing the different stages in the life-cycle of an insect, 

 for all these separate pieces of work on life-histories contribute towards the solution of 

 the great biological problems of distribution, adaptation to environment, parasitism, and 

 even add to the data on the questions of heredity and variation *. In order to arrive at any 

 knowledge of how to control injurious insects, it is obvious we must first learn the facts 

 of their life-histories, together with a knowledge o£ the distribution, food, enemies, 

 climatic needs, &c., vmtil its limitations can be outlined with approximate correctness — 

 then any steps taken to deal with it will probably be successful. This subject is at 

 present warmly debated in various parts of the world, and some contend that in the long 

 rim it is better to trust to Xature than to extensive artificial operations. My contention 

 is, that we may only trust to Nature when we have obtained a knowledge that will 

 warrant us in so doing, and that will probably enable us to restore natural conditions 

 when they have been abruptly infringed. 



Since my paper, above referred to, was published. Professor Antonio Bcrlese, of the 

 R. Scuola di Agricoltura, at Portici, has taken up this question and published two 

 important papers on the method of Economic Zoology ; and as he takes the same 

 view of the subject as I have done, I hope he may be successful in his effort to attract 

 greater attention to the economic importance of the parasites of Insects. 



III. Devjelopmext, and Structure in Early Stages. 



((') Egg. 



I have examined the ovaries of a large number of the flics immediately after theii" 

 emergence from the scales : thougli I cannot f say how lung the specimens had been iu 

 the imago condition inside the host, I found the eggs were present in the tubes in an 

 already advanced stage of development (PI. 11. figs. 2-5). It usually happened that the 

 ovaries became crushed so that the eggs were most of them free. I have not been able 

 to decide definitely whether tlie different stages of growth of the eggs are connected with 

 different positions in the egg-tubes ; but probably it is so, tiie egg nearest the oviduct in 

 each tube being the most advanced. Except those in the very earliest stages, the eggs 

 had the appearance of two masses of yolk connected by an isthmus ; it is clear that this 

 isthmus ultimately becomes the appendage of the perfected egg, which, as will be seen 



* A Germaa ecouomic entomologist, Dr. L. Ueh, of Hamburg, is at present engaged in enlightening public 

 opinion aa to the value of knowledge of this sort. 



t The reason why I am unable to say when the imago condition is reached, is because the creature is inside tlie 

 Coccid, and to expose it is to destroy it, and so no individual case can be traced. This ditKculty will always be met 

 with, and is insurmountable. From external signs it is possible to tell roughly when the creature pupates, heoausa 

 then it turns blacli, and this can be detected through the shell of the Coccid. Uut there is no such clue to the time 

 when the imago condition is assumed. 



