84 MR. F. BALFOUR-BROWNE ON THE LIFE-HISTORY 



make a loud, strident noise, which it does by rubbing the apex of 

 the abdomen against the underside of the apices of the elytra, in 

 which position is a file-like structure {vide PI. III. fig. 6). Both 

 sexes are alike in this. The beetle " squeaks " when it is alarmed 

 or annoyed ; for instance, when it is caught in the water-net or 

 held between finger and thumb. In my tumblers, if one 

 individual tried to seize a piece of worm upon which another 

 was feeding, the latter " squeaked," the squeak in this case 

 presumably being equivalent to the growl of a dog with a bone. 



3 (d) Sexual differences. 



There is very little difference in outward appearance between 

 the sexes, the larger tarsal pads of the male being about the only 

 one. The female is slightly la.rger than the male on the avernge 

 and perhaps slightly broader in proportion to length. 



(4) Life-liistory . 



The beetle is to be found in its habitat from March until 

 October. In the latter month it descends into the mud in the 

 bottom of the pond to hibernate, apparently remaining there 

 without moving, its legs and antennae folded in against the bod}', 

 until the following spring. Early in March, or possibly some- 

 times late in February, it reappears and towards the end of 

 March oviposition commences. 



4 (a) Oviposition. 



In t]\e laboratory my earliest date for the appearance of eggs 

 is March 23rd, but under natural conditions eggs are very scarce 

 until about the second week of April, when they become common. 



Whereas Dytiscid eggs are buried in the tissues of plants, the 

 females possessing piercing ovipositors, Pelohius eggs are laid 

 upon the surface of sub-aquatic vegetation. In m^^ tumblers and 

 tubs the eggs were laid in rows, end to end, sometimes as many 

 as eight to ten in a row, though odd eggs were also to be found. 



WJien about to oviposit the female lies along the plant stem, 

 clasping it with her legs so that the apex of her abdomen touches 

 the stem. The egg, which is blunt oval in form, J '5 mm. long 

 by '87 mm. bi'oad and equallj^ curved at both ends, is very clear 

 at the moment of extrusion and enclosed in a thin gelatinous 

 envelope which at once adheres to the plant. This envelope 

 quickly absorbs water and swells up into a thick protective 

 covering. 



Having laid an egg the beetle moves slowh' forward, waving 

 her antennpe in the water and usually touching the stem with 

 her palpi. She \noves just far enough to permit the next egg to 

 emerge so that it will touch the end of the previous egg, and in 

 this way she works along the stem, producing a string of eggs. 



