,266 MICROSCOPY FOR BEGINNERS. 



hatch in captivity. They are small, brownish, jelly 

 masses, which might easily be overlooked or passed by 

 as snails' eggs, often to be found in the same localities. 

 The newly-hatched young often bear but a slight re- 

 semblance to the parents, those of some genera having 

 but six legs, those of one species being said to have but 

 three. Many of these immature forms are parasitic on 

 aquatic insects, becoming free-swimming and independ- 

 ent when they attain adult growth and age. Some of 

 the mature mites are also parasitic in the gills of the 

 fresh- water mussel (Unio}. On account of these pecu- 

 liarities the study of their life history is a difficult one. 



The Entomostraca and Infusoria are said to form 

 their favorite food. 



There may seem to be but little connection between 

 the water-mites and the water-bear, and still less resem- 

 blance, yet naturalists have classified them near together. 

 The water -bear (Fig. 172) is a common and curious 

 aquatic animal, so closely and so comically resembling a 

 transparent eight-legged microscopic bear that the be- 

 ginner will know it the first time he sees it ; further ref- 

 erence to it is therefore reserved for another page 

 (p. 267). 



Key to Genera of the Water-mites (Hydrachnidce). 



1. Body colorless, cylindrical, elongated, and transpa- 

 rent ; legs eight, short, with claws ; the animal 

 walks slowly and is bear -like in appearance. Wa- 

 ter-bear (Macrobi6tus\ 1. 



