spatial Relations 



329 



feed, and find more oxygen. The larva of Dixa is one 

 of the most interesting of these. It will float in the 

 surface film, but not for long, if any support be at hand. 

 Touching a leaf it immediately bends double, and 

 pushes forward by alternate thrusts at both ends, until 

 it has lifted a film of water to a satisfactory level. 



On the surface are deposited the eggs of many insects 

 having aquatic larvs, but these eggs are heavier than 



water, and unless anchored to 

 some solid support or buoyed 

 up with floats (as are such eggs 

 as those of Culex and Core- 

 thra) nearly all of them settle 

 to the bottom. There are, 

 however, a few midges whose 

 egg-clusters float freely. A 

 brief account of the egg-lay- 

 ing of one of them, Chironomus 

 meridionalis, will illustrate 

 several points of dependence 

 on the surface tension. 



The female midge, when 

 ready to lay her eggs, rests 

 for a time on some vertical 

 stem by the water side in the 

 attitude illustrated in figure 

 194. She extrudes her eggs 

 which hang suspended at the 

 She then flies over the water 

 carrying them securely in a rounded climip of gelatin. 

 After a long preparatory flight, consisting of cotu-sing 

 back and forth in nearly horizontal lines at shoul- 

 der height above the surface of the water — a per- 

 formance that lasts often twenty minutes — she 

 settles down on the siu-face and rests there with 

 outspread feet. The usefulness of her elongate tarsi is 



Fig. 193. Larva of a Dixa 

 midge, inverted, to show: u, 

 caudal lobe; b, creeping 

 bristles; c, prolegs. The 

 arrow indicates the direction 

 of locomotion, middle fore- 

 most, both ends trailing. 



tip of the abdomen. 



