The egg-mass when first laid is i mm. in diameter, and in the 

 case of an unfertilized female they remained this size, but the fertile 

 egg-masses found in the water are 1-5 mm. across. 



The egg. Each mass contains from 80-90 eggs arranged apparently without 



any order. The egg-shell is quite transparent and the developing 

 embryo is clearly seen enclosed within the vitelline membrane, which 

 is not in contact with the shell at the two ends of the egg. The 

 characteristic antennae of the larva can be easily seen in the egg ready 

 to hatch, and by this means the eggs can be distinguished from those 

 of other Chironomids. The egg is very slightly kidney-shaped, strongly 

 convex on the dorsal surface, and very slightly concave on the ventral ; 

 viewed dorsally it is oval. In size it is '16 mm. long by '06 mm. broad. 

 It differs from the egg of C. dorsalis in being smaller, relatively broader 

 and more convex. 



The development of the embryo within the egg takes about six 

 days. If we now examine one of these eggs just ready to hatch, we can 

 make out the more important features of the larva. In the transparent 

 head we can recognise the antennae, eye spots, mandibles and labium ; 

 while the prothoracic appendages are very conspicuous. The body is 

 very much coiled up, as it has to be compressed into nearly half the 

 space it will occupy on emerging from the egg; however, many of the 

 segments can be counted and sometimes the anal setae are visible. 

 It may be worth while to mention here, that on the fourth day of 

 incubation the double eye spots are sufficiently visible to enable the 

 eggs of a Chironomus to be distinguished from those of a Tanypus, the 

 eyes of the latter being single and kidney- or cornet-shaped. However, 

 there are one or two species of Chironomus (Nos. 13 and 14 Appendix) 

 in which the double eye-spots are completely fused into single masses, 

 so this test is not absolutely final, but it is of great use in examining 

 miscellaneous egg masses. 



Hatching Larvs. The embryos about to hatch become very active within the eggs, 



and may be seen to revolve on their longitudinal axis two or three 

 times a minute, until at last the egg shells burst and the larvae are set 

 free. They take about a minute to extricate themselves from the shell, 



