OF THE WATER-BEKTJiK PELOBllJS TAllUUS. 85 



I tiiouglit jvt iii'st tliat the beetle jiulged her distance by inean.s 

 of the palpi feeling their way, but, as I have mentioned, these 

 organs do not invavitibly keep contsict with the stem, while the 

 gonapophyses do, so that it appears as if these latter decide how 

 far forward the beetle is to move after depositing an egg. 



I have not been able to determine the total number of eggs 

 laid by a female, the greatest number of which I have a record 

 being twenty ; neither do I know whether an individual lays all 

 her eggs during one short period or whether she lays a number 

 of batches. 



The period of oviposition for the species is a long one, lasting 

 from March until July. I have not actually found eggs later 

 than June 15th, but 1 have found very young larviB in August 

 under rather interesting circumstances. 



On August 5th, 1915, in a disused chalk pit at Beckham in 

 East Norfolk, where there were several shallow clear-water 

 ponds, I found various stages of the beetle. There were old 

 males and females, newly-emerged soft males and females, full- 

 grown larvae and a few larvae not more than ten days or a 

 fortnight old. As incubation in the warmest period of the year 

 occupies only nine days, the eggs from which these larvaj hatched 

 must have been laid in July. 



4 (b) Incubation. 



The earliest laid eggs took twenty-five days to hatch, but the 

 incubation period gradually became shorter until, in June, nine 

 or ten days became normal. Eggs laid early in April and 

 placed in an incubator at summer temperature liatched in nine 

 or ten days, so that temperature is evidently the controlling 

 factor in the length of the incubation period. I shall return to 

 this point later on. 



8o far as I can find, there is no special hatchnig appai-atus 

 sucli as that in the larva of Dyiiscits (1 ), the shell ripping from end 

 to end along an irregular line and apparently always along the 

 ventral side of the embryo, however it may happen to be lying 

 in the egg. A small pair of spines are certainly visible on the 

 head bet\veen the eyes, near the position of the hatching spines 

 of DijUscus lap2)onicios, but they are not functional, as is evident 

 from the manner in which the shell rips, and I imagine that, if 

 anything weakens the latter along the breaking line, it must be 

 the tarsal claws. 



4 (c) Vital Staining oftjie Embryo. 



In order to observe the developing embryo I removed many of 

 the eggs from the water-plants upon whicb they had been laid 

 and kept them upon cotton-wool saturated with water. I have 

 used this method with the eggs of several other water insects— 

 e.g., Agrionid dragonflies and others, Banatra linearis, and 



