642 THE MICROSCOPE. 



Dr. Eobins, found spinning a white silken web on the base 

 of the sparrow's thigh, or on the fore-part of its body ; on 

 raising this delicate web, you perceive that it is filled with 

 minute eggs, from, which the young issue, being in due 

 time hatched by the warmth of the body it is destined to 



annoy. In fig. 296 are 

 seen some eggs of a 

 parasite infesting the 

 hornbill ; they are 

 glued to the feathers 

 near the head of the 

 bird ; the Iarva3 are 

 ready to leave the egg 

 in two days. Another, 

 curiously enough, se- 

 lects the pultnonic ori- 

 fice of the snail : when 



Fig. 296.-ZonE of the Parasite of Hornbill. the an i ma l Dilates this 



orifice, for the purpose of allowing the air to penetrate its 

 respiratory cavity, the female acarus slips through the open- 

 ing, and lays her eggs in the folds of the mucous membrane, 

 where they are gradually developed. The young, upon 

 issuing forth from the eggs, select some portion of the 

 snail's body upon which to feed and perfect their growth. 



Ixodidce are furnished with a powerful rostrum, armed 

 with recurvate spines, with which they pierce the skin of 

 the unfortunate animal upon whose blood they live. So 

 firmly do these anchor-like organs retain their hold, that if 

 the parasite is pulled away it usually carries a portion of 

 the skin of its victim with it. These creatures live upon 

 a great variety of animals. The dog is very liable to their 

 attacks, and many species fix themselves exclusively upon 

 serpents and other reptiles. Glyciphagus cursor is found 

 in the feathers of the owl, and in the cavities of the bones 

 of skeletons. Gamasidce are furnished with a sucking 

 apparatus very similar to that of Ixodidce, usually attaching 

 themselves to the bodies of beetles; the common Dung- 

 beetle (Geotroupes) is often found with its lower surface 

 nearly covered with them. 



There are other families leading a more active Ufa, 

 being furnished with eyes. One family, Hydrachnidce, 



