172 



ANIMAL PARASITES AND MESSMATES. 



edeae, if not all of them, are, when young, parasites 

 of certain hymenoptera," says Mons. Fabri, who has 

 watched with rare Bagacity the obscure and interesting 

 habits of these microscopic assassins. 



The Sitaris hwmeralis has a progressive develop- 

 ment at first, a recurrent one afterwards, and then again 

 it becomes progressive. 



Aphides which are not yet full grown, and which 

 arrest the exuberant vegetation of certain plants, are 

 in their turn attacked by an insect which is by no means 

 lukewarm in its proceedings. A small species of cynips 

 (AUotria victrix) lays its eggs, like an ichneumon, in 

 the body of a rose aphis, and multiplies rapidly at their 

 expense. (Westwoodl. 



There are certain flies which are not more delicate in 

 their mode of life than the preceding insects. We allude 

 to the (Estri. We give the representation of the species 

 which attacks the horse. 



Hinder part. 



36. — CEstrus of the Horse 



Anterior part. 



Instead of making their attacks on those of their own 

 class, the gadflies prefer to instal themselves on mam- 

 mals and sometimes even on man. Fortunately their 

 wants are not very great ; they are contented with a 



