281 



BIOIvOGY* AND TAXONOMY 



The Bgg Stage 



The eggs of Chirunoniidcc, with the exception of those species be- 

 longing to the terrestrial forms in Ceratopogonince, are deposited in 

 water, principally in pools or slow-flowing streams. At times they may 

 be deposited in indoor aquaria, or other suitable receptacles having an 

 accessible water surface. There is considerable variation in the form 

 of the ^gg mass in the different species, but in all recorded cases the 

 eggs are enveloped in a gelatinous outer covering, and may take the 

 form of a pear-shaped mass, be arranged in rope-like tubes, or be 

 massed closely together, forming large groups. In one case observed 

 in the Illinois River the eggs of Cricotopns trifasciahis Panzer were 

 grouped together, forming a large elongate mass about ten inches long 

 and from one to two inches in diameter. Miall and Hammond give 

 an account of the various Qgg masses which they have examined. f I re- 

 produce the passages here. "The various forms of tgg rope which 

 characterize different species of Chironomus reach a climax of com- 

 plication in C. dorsalis. In simpler cases the eggs may be enclosed in 

 a globular or pear-shaped gelatinous mass, which is glued to a stone 

 in the bed of a stream. Or the eggs may lie, almost at random, within 

 a gelatinous pipe. Both a pipe, enclosing the eggs, and an outer gelat- 

 inous envelope may be present, and the pipe may be thrown into bends 

 or spires which do not affect the outer covering. Lastly, a pair of in- 

 terwoven cords may be added, which traverse the cylinder, on whose 

 outer wall lie the spires of the egg-containing pipe. The tgg masses 

 may contain three different kinds of gelatinous substance, one forming 

 the pipe, a second the general investment, a third the interwoven cords. 

 The two latter may be furnished by the gluten-gland, whose cavity 

 when cut across shows sectors of what are probably two different se- 

 cretions; the wall of the egg-pipe is perhaps secreted by the ovary or 

 oviduct. 



"Since the larvse wdiich have to issue from the eggs have to live in 

 water, it is convenient that the egg-chains should be laid in water, and 

 further that they should float at the surface, where they can be freely 

 supplied with air, and run no risk of being smothered by silt or or- 

 ganic refuse. If the w^ater were stagnant, the eggs might float free, 

 as the egg-raft of the gnat does, but the eggs of Chironomus dorsalis 

 are laid in slow streams, and must be secured, lest they should be 

 swept aw^ay, and perhaps lodged in some unsuitable place, or even car- 



*Notes on the biology of Chironomus viridicoUis, a species often present in reser- 

 voirs for the supply of city water are yivoii on i)p. 4.19-4G3. 

 tThe Harlequin Fly, pp. 154-155. 1900. 



