28 MICROSCOPIC OBJECTS. 



Acari. — This small tribe of creatures has not only fur- 

 nished employment to the microscopist of olden times, 

 when examining a morsel of decayed cheese, but of late 

 years has afforded an important subject for discussion ; 

 the animals supposed by Mr. Crosse to be producible by 

 galvanic agency being a species of this genus. When 

 carefully examined, their structure is seen to be very dif- 

 ferent from that of insects. Among the most curious is 

 a species which infests the Dung Beetle, found among the 

 small heaps of manure left by cattle in fields. These 

 beetles have hard smooth poHshed corslets and elytra; 

 and the small Acarus found in the folds between the head 

 and the body (for beetles are said to have no neck) is 

 provided with a very curious appendage to each of its 

 feet, by which it can produce a vacuum, and thus w^ith 

 ease move about on the pohshed surface of the beetle. 

 To examine the structure of the foot, place under the 

 microscope a few Acari in an aquatic box, vnth a magni- 

 fying power of about 80 diameters, when the action of 

 this suction apparatus may be readily observed as the 

 creatures crawl upon the glass of the hve-box. 



Aerating Leaflets of the Larva of the Lihellula. — These 

 beautiful microscopic objects are the tails of the aquatic 

 larva above named, and when mounted in Canada balsam 

 are permanent objects. In shape they resemble the leaf 

 of the lam-el ; and when examined under a power of 30 

 diameters, the two large tracheae which run along the 

 middle, and their numerous branches, are readily seen. 

 With a magnifying power of 100 diameters, the spiral 



