114 THE CANADIAN ENTOMOLOGIST 



Ihe mistake was made of attempting to rear the nymphs in 

 small jars. Whether on account of lack of sufficient oxygen or of 

 appropriate food, or too high a temperature or some other unknown 

 cause, the greater number of nymphs perished as soon as hatched. 



The remnant were transferred to a large aquarium used for 

 breeding mussels. This was a zinc-lined tank about two feet deep 

 and with a supeificial area of thirty or thirty-five square feet, with a 

 layer of soft mud in the bottom and an overflow arrangement by 

 means of which a quiet but constant stream of fresh water was kept 

 circulating through the tank. There were a number of mussels in 

 the mud and several crayfish. A few water weeds supplied shelter 

 for smaller organisms, of which a large Ostracod was the most 

 plentiful. I observed several of the older nymphs feeding on the 

 Ostracods, and it is possible that the absence of some similar food 

 caused the individuals in the separate jars to die. 



The newly-hatched nymphs are very active and, as a rule, keep 

 close to the bottom. They are negatively phototropic until the 

 fourth or fifth instar and this condition, which keeps them in the 

 shadows, aided by their great transparency, is doubtless of much 

 value in enabling them to escape their enemies. The bulk of the 

 eggs hatched July 8. The first moult (second instar) occurred about 

 July 1 6th, the second about July 24th, the third. July 31-Aug. 3, the 

 fourth, August loth, and the imagos appeared about August i8th. 

 From the third instar on, the mortality was high. In the morning, 

 numbers would be found on the surface of the water near the edge 

 held by a bubble of air, the buoyancy of which they were unable to 

 overcome and, unless assisted, they perished in this way. It seems 

 probable that they *re most active at night as they were rarely seen 

 to dart to the surface frequently, except on dull, dark days. 



The Egg. 

 Length •about 9 mm. Breadth about 4 mm. Shape elongate- 

 oval, bilaterally rather than axially symmetrical, i.e., one side nearly 

 straight, the opposite strongly curved. (See Fig. i.) Colour grayish 

 yellow (later stages only were observed); the surface ornamented 

 with a delicate tracery in the form of interlocking hexagons like a 

 honeycomb or the facets of a compound eye. The egg is fastened 

 in a sort of shallow cup which is of a lealhery texture and dark 

 brown in colour. The distal end through which the nymph emerges, 



