Objects for the Microscope. 147 



Birds have many varieties. 

 The Pheasant-louse ; 



The Parasite of the Rook and Chaffinch, called Ricinus 

 pavonis, are interesting objects. 



THE ACARI, OK TICKS, MITES. 



These parasites are found on animals, birds, and insects. 

 They belong to the lowest order of Arachnida, the Spider 

 tribe, and many of them are beautiful microscopic objects. 



The Acarus scabici, or itch insect, is a very valuable pre- 

 paration. It is the occasion of that disgusting disease the 

 Itch, and is exceedingly difficult to obtain. It lodges in a 

 burrow near the pustule ; but, being scarcely visible to the 

 naked eye, is rarely extracted in a perfect state. When 

 examined under the microscope it is found to have an oval 

 body, a mouth of conical form, and eight feet terminated by 

 bristles. The head has five strong mandibles, with which 

 it cuts out a little nest under the skin ; it lays many eggs, 

 and is most difficult to eradicate. 



ACARUS DOMESTICUS, OR COMMON CHEESE-MITES. 



The dust of decayed cheese is composed entirely of these 

 mites, their eggs and their excrement. Mounted properly, 

 we should see their oval body, with a head from which 

 extends two large mandibles, somewhat resembling the 

 claws of a lobster. When the insect is in repose it crosses 

 these mandibles over its head, forming a kind of roof over 

 the mouth. The legs are reddish, and inserted in two 

 different groups, the anterior pair considerably larger in 

 the male. 



These Acari are both viviparous and oviparous. 



ACARUS PASSULARUM, 



found abundantly in dried figs, is like the cheese-mite, but 

 has very long bristles at the sides of the mouth. 



