176 AQUATIC MICROSCOPY FOR BEGINNERS. 



convex, usually bearing spines, prickles, or scales. 

 Chmtdnotus . II. 



a. Tail not forked (b'). 



b. Posterior extremity often bearing finger-like ap- 



pendages, never long, coarse bristles (c). 



b. Posterior extremity rounded, often bearing long 



bristles; animal free-swimming, movements 

 swift. Dasydytes, III. 



c. Body entirely and finely ciliated, usually flattened, 



not divided into distinct segments or rings. 



Turbelldria, IV. 

 c. Body smooth, without cilia, bristles or spines, 



worm-like; posterior extremity pointed. Augutl- 



lula, V. 

 c. Body elongated, divided into segments or rings, 



with bristles, podal spines or both. Oligo- 



ckceta, VI. 



I. Chir6nomus larva (Fig. 133). 



Chironomus larva has a worm-like, more or less seg- 

 mented, colorless body, eight or nine times as long as 

 wide, a large head, the mouth parts usually being dis- 

 tinctly apparent. The four short rudimentary leg-like 

 appendages are in pairs on each end of the long body, 

 the brownish hooks, or strong curved bristles on their 

 extremities being more or less retractile, while in 

 some forms two clusters of long bristles spring from 

 the upper surface near the posterior border of the ani- 

 mal. The perfect insect into which this larva will de- 

 velop is a two-winged fly resembling the mosquito. 

 These are often seen in great numbers above the ponds 

 and marshes. The species are numerous, but have 

 never been studied by American entomologists. 



