20 THE CANADIAN ENTOMOLOGIST. 



^nd are replaced with fertile ones. This takes place as late even as the 

 eighth day of incubation. 



The duration of incubation is from ten to twelve days, at the end of 

 which time the egg-cases and adhesive nidus that holds them are cast off 

 entire, providing there be no late-laid eggs, in which instance the whole 

 mass, including empty eggs and nidus, remain attached to the back of the 

 male until the last one is hatched. And just why it is that a few unfertile 

 eggs will drop away from among the mass of fertile ones and leave the 

 parent before incubation is complete, whereas, on the other hand, the empty 

 egg cases and nidus remain until the very last laid egg is hatched, I cannot 

 understand. 



The eggs are a long oval, five mm. long by one mm. thick, and are 

 the same colour as the parent bug. The cast-off nidus and egg cases 

 resemble a knobbed shield as nearly as anything that I can think off, being 

 an oblong oval, with concave surface to back of parent. 



During the period of incubation the male spends much of his time in 

 aerating the eggs. This is done by gently raising and lowering the wings 

 so that the air taken in at the surface, and held under the wing-cases, is 

 moved back and forth beneath the mass of eggs, which take it up little at 

 a time, as the needs of incubation require. The adhesive nidus into which 

 the eggs are set must perform the same ofiice or function for the gestating 

 insect that the placenta in warm-blooded creatures performs for their 

 gestating young, with this difference, that in warm-blooded animals air is 

 taken into the blood from the lung?, and transferred to the placenta 

 through the circulation, while in the creature under discussion the air is 

 absorbed directly through the pores of the wing-sheaths. 



At the end of incubation the male comes to the surface, and with his 

 back partly out of the water, the young begin to appear. 



The first thing seen after the rupture of the egg. case is the beady- 

 black eyes, llien the male continually raises and lowers the wing-sheaths 

 and executes a jerking motion along with it, at regular intervals. The 

 young insect is extruded from the egg-case by easy stages, and in a 

 manner very similar to the birth of a mammal. I am not sure whether the 

 power of extrusion lays wholly in the eggcase or not, but incline to the 

 belief that some pneumatic pressure is brought to bear on the fo:'al insect 

 from the air beneath the wing-sheaths of the male, which is ke])t in 

 constant motion, and which of necessity must exert more or less pressure. 



