i8 Outline of Life-history 



' The eggs are laid in a jelly-mass, about 250 being 

 counted in one instance. The row of eggs is contained 

 within a hollow gelatinous rope of firm consistency. The 

 egg-rope is bent into a series of frequently reversed loops, 

 and its two ends are approximated, so that it is horse- 

 shoe shaped. The whole is enveloped in a mass of much 

 softer jelly. The larvae hatch out in about five days, and 

 escape into the hollow egg-rope. By the end of the first 

 day after hatching they become altogether free and take 

 up their abode in the Spirogyra. They select a point 

 where several filaments intersect, and begin building their 

 case. This at first is of very irregular form, but by the 

 third or fourth day it assumes a tube-like character. 

 structural " The full-growu larva measures ten to twelve mm. in 



peculiari- 

 ties of Or- 

 thoelailius. 



Fig. 10. — Pupa of Cliironomus (Orthocladius). x 12. 



length. The general colour is pale green, and the green 

 food in the alimentary canal is cons^Dicuous. Four anal 

 blood-gills are present, while those of the ventral series 

 on the penultimate segment are wanting. The paired 

 sensory filaments are set on short stalks, and each consists 

 of six long bristles. The tracheal system is well developed, 

 and in this connexion the well-aerated habitat of this 

 larva may be mentioned. The longitudinal tracheae are 

 much larger than in C. dorsalis ; they are relatively wide 

 in front, but narrow backwards. Numerous segmentally 

 arranged branches are given off. The epithelium of the 

 main tracheal trunks shows a purple colouration. Two 

 thoracic intersegmental and eight abdominal intra- 



