THE STUDY OF FRESH-WATER ANIMALS. 181 



INSECTA. The following belong to the Class Insecta: 

 Water beetles, Whirligig beetles. Order: Coleoptera. 

 Though aquatic these beetles breathe air directly from the 

 atmosphere ; they are carnivorous. 



Pond skaters belong to Order Hemiptera or Bugs. 

 They have a long needle-like boring and sucking append- 

 age below the head; it is pushed into dead insects, etc., 

 and juice extracted therefrom. Water Boatmen belong 

 to this order of Bugs. 



Griiats. These are true flies. Order: Diptera. These 

 spend their larval and pupal stages in the water ; their 

 adult life is aerial. All stages have aerial respiration. 

 (For characters of the foregoing Insect Orders see 

 p. 166.) 



Caddis-fly larvae. Order: Trichoptera. These larvae 

 usually inhabit cases made of twigs, leaves, sand grains, 

 etc. They have aquatic respiration. The adults have 

 four hairy wings ; the fore wings are usually longer and 

 narrower than bind wings. 



Stone-fly larvae. Order : Platyptera. These larvae have 

 usually paired tufted gills upon the hind body. Found on 

 stones in running water. 



Mayfly larvae. Order: Plecoptera. Older larvae with 

 paired gills upon hind body. Younger stages breathe by 

 skin. In muddy bottom of streams, etc. Adults do not 

 feed. 



CRUSTACEA. Water- fleas, Fresh- water Shrimps. These 

 are members of the Class Crustacea. In fresh-water pools 

 there are three common types of water -flea, all of which 

 are likely to occur in school aquaria, viz. Cypris, Cyclops, 

 Daphnia. The popular name "flea" is probably due to 

 the jerky movement by which they progress in the water 

 as well as to their small size ; they are, as already indi- 

 cated, not insects. They have two pairs of feelers, one 

 pair of which is used in swimming. The fresh-water 

 shrimp (Gammarus) is a higher type of Crustacean. It has 

 a laterally compressed body and breathing appendages on 

 its legs. 



