Microscopical Essays, 



267 



of gum, by which they are connected and bound together, is very 

 vifible in many places ; they ftrengthen this connection further, 

 by filling up all the intervening fpace between the eggs with a 

 very tenacious fubftance. The eggs are cruftaceous, and fimilar 

 to thofe of the hen. Fig. 3, Plate X. is a vertical fection of 

 the eggs, mewing their oval ftiape. Fig. 5 is an horizontal 

 fection through the middle of the egg. It is not eafy to defcribe 

 the beauty of thefe objects, when viewed in the lucernal micro- 

 fcope ; the regularity with which they are placed, the delicacy of 

 their texture, the beautiful and ever-varying colours which they 

 prefent to the eye, give the fpectator a high degree of rational 

 delight, 



Some depofit their eggs in the back of other infects ; thefe, 

 after having pa fled through their various transformations, become 

 what is termed an ichneumon fly. In the Lapland Alps there is 

 a fly covered with a downy hair, called the rhen-deer gad-fly, 

 oeftrus tarandi, Linn. It hovers all day over thefe animals, 

 whofe legs tremble under them • they prick up their ears, and 

 flee to the mountains covered with ice and fnow, to efcape from 

 a little hovering fly, but generally in vain, for the infect but too 

 foon finds an opportunity to lodge it's egg in the back of the 

 deer ; the worm hatched from this egg perforates the fldn, and 

 remains under it during the whole winter ; in the following year 

 it becomes a fly. The oeftrus bovis is an equal terror to oxen ; 

 the hippobofca equina to horfes ; oeftrus ovis * to the (beep, &c 



Kk 2 The 



# Oeftrus ovis in nafo five firm frontis animal ium rumenantiurrK 



