284 AQUATIC MICROSCOPY FOR BEGINNERS. 



and 197 there are four groups, formed of two coxse 

 each; in Fig. 193 there are six groups, the anterior 

 alone being formed of two coxae, the two posterior 

 groups on each side being of but one coxa each and 

 separated. Their shape differs widely even in the spe- 

 cies of one genus; their arrangement, however, is con- 

 stant and important. 



The eight legs are long and jointed, the last joint . 

 ending in one or two short claws. The hairs fringing 

 their margins are long, numerous, and are used as aids 

 in swimming. They add a good deal to the beauty of 

 the animal. 



Mites are found in salt-water as well as in fresh, but 

 with the marine forms this little book has nothing to do. 



The fresh-water forms are propagated by means of 

 eggs, which are often seen attached to the stems of 

 aquatic plants or to the lower surface of floating 

 leaves, where the writer has obtained them and had 

 them to hatch in captivity. They are small, brown- 

 ish, jelly-masses, which might easily be overlooked or 

 passed by as snails' eggs, usually to be found in the 

 same localities. The newly-hatched young often bear 

 but a slight resemblance 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 independent 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 peculiarities the study of their 

 life history is a difficult one. 



The Entomostraca and Infusoria are said to form 

 their favorite food. 



