114 



surface of the water, all the eggs sink to the bottom of the vessel, 

 which accounts no doubt for the in-egular periods of incubation. Of 

 the 40 eggs deposited during the night of April 30 a few hatched on 

 May 15, others hatched on May 30, and still others of the same brood 

 on June 10. It will be seen from this that a wide range obtains as to 

 the incubation period (from fifteen to forty days). 



The larv£e are active at the surface of the water for the fii'st twenty- 

 four hours, after which they move to the bottom when disturbed, and 

 can there remain as long as forty-seven minutes without coming to 



Fig. 1. — Cimehyliaslesmu»icm: egg, at left; lar- Fig. 2. — Conchyliastes musicue: head of larva above; 

 va, in middle; pupa, at right; all enlarged inner mouth-parts of larva helow; much enlarged 



(drawn In Division of Entomology). (drawn in i)lvision of Entomology). 



the surface for air. Larval growth is very rapid, most of the speci- 

 mens bred reaching the pupa condition in five dajs (120 hours), though 

 as long as seven days have been spent in this condition. 



The larvae are not "wigglers " in the ti'ue sense of the tei-m. They 

 jerk characteristically when suddenly disturbed, but ordinarilj' move 

 from the top to the bottom of the vessel at an angle of about 45 degrees 

 with little motion save the rapid movement of the oral cilia. The 

 passing of the larvae from the top to the bottom of the water with 

 apparently little effort gives them a graceful appeai-ance. While at the 

 bottom of the glass they catch large bundles of Spirogyra, which are 

 broken into smaller pieces as the surface is approached. The vertices 



