114 



surface of the water, all the egg.s sink to the bottom of the vessel, 

 which accounts no doubt for the irregular 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 larvffi are active at the surface of the water for the first 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. — Conchyliastesviustcvs: egg, at left; lar- 

 va, In middle; pupa, at right; all enlarged 

 (drawn in Division of Entomology). 



Fig. 2. — Conchyliastcs musicus: head of larva above; 

 inner mouth-parts of larva below; much enlarged 

 (drawn in Division of Entomology). 



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

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

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



The larvfe are not "wigglers" in the true sense of the term. The}^ 

 jerk characteristically when suddenly disturbed, but ordinarily move 

 from the top to the l)ottom 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 larvpe from the top to the Ijottom of the water with 

 apparently little effort gives them a graceful appearance. While at the 

 bottom of the glass the}^ catch large bundles of Spirogyra, which are 

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



