PREFACE. 



The subject treated in the following chapters, Agricultural 

 Zoology, has perhaps been more neglected in England than any 

 other branch of science applied to agriculture : even the name 

 itself is hardly at present understood. It is true, indeed, that 

 the labours of Curtis, and in later years of Miss Ormerod, have 

 developed one branch of economic zoology — namely, the part 

 played by insects in causing disease amongst animals and plants ; 

 it is true also that some of our veterinary surgeons have done 

 excellent work on the other parasitic diseases of animals ; but 

 there remains a vast portion of the subject that has neither 

 gained the attention of English scientific men nor been siun- 

 marised in an English text-book. Agricultural Zoology treats 

 of the life-histories, the habits, the peculiarities of all the 

 animals which affect for good or for evil our stock and crops, 

 whether on the farm or in the garden, and the structure and 

 development of domestic animals. Parasitism plays an im- 

 portant part in this subject, especially in the worms ; but the 

 economic effects of parasites are not confined to worms — the 

 parasitic insects, the minute protozoa, equally take their annual 

 and preventable toll of our flocks and herds. "Nor, again, is 

 parasitism always an injurious phenomenon : its beneficial effects 

 are equally marked and equally under control, given only the 



