THE SHEEP-TICK. r39 



can be found without difficulty upon almost any sheep ; hut to 

 get it away without damaging it is not a very easy task, the 

 hooked and powerful legs grasping the wool as if with six pairs 

 of pincers, and the insect pushing its way deeper and deeper 

 in the fleece as it thinks itself in danger. While thus enoaoed 

 in evading the pursuer, the Sheep-tick looks so very much like 

 a spider tliat the PVench call it the Spider Fly. 



The whole structure of the head and beak of this insect is 

 very remarkable, and it is not very easy to trace the analysis of 

 the various parts of the mouth. If one of these insects be 

 examined with a microscope, the front of the head is seen to 

 be furnished with two rather long, curved, pointed, horny 

 plates, covered with bristles, between which lie the setoe or 

 piercing organs. Mr. Westwood thinks that these instruments 

 are intended for the purpose of pushing away the hair "f the 

 animal on which the Fly is feeding, so that the seta3 may 

 penetrate the more deeply into the skin. 



It is evident that these projecting horny processes would be 

 \ery much in the way of the Sheep-tick when it travels to and 

 fro through the wool. If, however, the insect be turned over, 

 so that the under surface can be seen, the mode in which tliis 

 difficulty is overcome is at once evident. On the under surface 

 of the thorax there is a deep pit, extending beyond the fore- 

 legs as far as the base of the middle pair of legs. When the 

 head is bent downwards, the two horny projections, together 

 with the piercing and sucking apparatus of the mouth, are 

 sunk completely into the pit, so that nothing is presented to 

 the wool but a perfectly smooth and shining surface which can 

 easily glide between the fibres. 



The colour of the Sheep-tick is yellow-brown, and the thorax 

 and limbs are polished and granulated. The legs are re- 

 markably strong, and tlie claws are jet-black and shining. 

 In shape they very much resemble the incurved claws of the 

 sloth, and the analogy between them is carried out in their 

 action as well as in their forna. Just as the hooked claws of 

 the sloth enable it to move with great activity among the 

 branches, swinging itself from bough to bough as easily as dov-'s 

 a monkey, so do the similar claws of the Sheep-tick enable 

 the insect to traverse the thick wool, among the fibres of 



