760 Mr. Frank Balfour Browne [May 9. 



The pupal stage lasts about three weeks, and the only change 

 noticeable during that time is a slight pigmentation of what is at 

 first a perfectly white pupa. At the end of the pupal stage the skin 

 ruptures along the back, and the perfect insect comes forth at first 

 white and soft, but in the course of two or three days it assumes its 

 normal coloration, and after a longer period its normal hardness. 

 After a week or so it makes its way out of tlie pupal cell by biting 

 and scraping, and at once goes to the water. 



In its native haunts it spends most of its time amongst the stones 

 and mud at the bottom, occasionally coming up to renew its air- 

 supply, and in my tubs also it was seldom to be seen. 



With regard to its winter habits, it apparently buries itself at the 

 bottom of the loch as soon as the cold weather begins, and sleeps 

 until the following spring. In my tubs it disappeared completely in 

 October or November, burrowing deep into the soft oozy mud at the 

 bottom, and there it remained until the following March. During 

 all this time the metabolic processes must be practically at a stand- 

 still, as otherwise the insect would require to renew its air-supply at 

 frequent intervals. 



Having now outlined the life-history of this type of the swimming 

 cai-nivorous water-beetles, I will take an example of the other group, 

 and the one I have chosen goes by the name of Hydrocharifi cara- 

 hoUks. There is only one species of Hydrochark in the British 

 Islands, and it is practically confined to the south-east of England, 

 only very occasionally having been found anywhere else in the 

 country. It inhabits stagnant ponds and drains, and is not uncommon 

 in a few places in Surrey, Essex, and Middlesex. 



T began to experiment with it five years ago in the north-east of 

 Ireland, having obtained my specimens from kSurrey. Each year I 

 obtained eggs, reared the larvaj, and renewed and increased my stock, 

 so that it is obviously not the climate of north-eastern Ireland wliicli 

 prevents this species from being a native there. 



Tlie conditions in my tubs were just such as are to be found in 

 any ])ond or drain in the country, and apparently the only reason 

 why this s})ecies is confined to the south-east of England is that 

 com]X'ting si)ecies prevent it from extending its range. 



A\'liereas Dj/tkcm lays its eggs singly in holes pierced by it in 

 tlie living vegetation, Hydrochark builds an elaborate silken cocoon 

 whicii floats in the water, and in which about fifty eggs are deposited. 



The Hpinniny of the cocoon is a wonderful process. The beetle 

 carries on its underside a film of air, which is part of its supply for 

 breiithing. The cocoon is actually spun on a part of this film of 

 air, which is then detached from the rest of the film as a bubble en- 

 closed in silk. The egg-l;iying connnences soon after the cocoon is 

 begun, and the eggs are arranged side by side in the cocoon standing 

 u]H)n one end, bring fastened in position by silken threads. A space 

 al)o\c the eggs is tilled with very loosely woven silk. 



