1913] on The Life-History of a Water-Beetle 755 



has quite simple front legs. The slide also shows a full grown larva, 

 and thus gires an idea of the relative sizes of these two stages of the 

 species. 



This species is extremely local in the British Islands, only having 

 been found in a few localities in Scotland, and in one in north-west 

 Ireland. It inhabits lochs, usually mere lochans, at altitudes of from 

 800 feet upward, and there are certain characteristics about its habitat 

 which make it possible generally to tell at a glance whether a par- 

 ticular lochan is or is not likely to hold the species. 



As a rule the habitat is a bare stony lochan, with very little vegeta- 

 tion ; it has no stream flowing into or out of it, and trout and 

 lapponicvs are mutually exclusive. There are usually newts and 

 fresh-water shrimps {gammarus), but otherwise there is always a 

 marked scarcity of animal life. Very few other water-beetles are 

 associated with lapponicus, which usually is abundant where it 

 occurs. 



The only place I have found the species in great abundance is in 

 a lochan 950 feet above sea-level on the island of Eigg. Along its 

 eastern side this lochan is strewn with large stones, and under these 

 the beetle is to be found, often as many as four or five under one 

 stone. It occurs in other lochans on Eigg, and has been found also 

 in Rhum, Skye, Mull and Arran, but otherwise it is only known from 

 Inverness-shire. 



One place in Mull where it used to occur abundantly is a pecuUar 

 loch, situated in the top of a hill, about 800 feet behind Tobermory. 

 The place looks like the crater of a volcano, but I believe is not so 

 described by geologists. The species has apparently quite disappeared 

 from this loch ; it is probably slowly disappearing from our islands, 

 being a remnant of the fauna which abounded when our climate was 

 much colder than it is at present. 



All my specimens came from the one lochan on Eigg, and they 

 were placed in large tubs in my garden in the north of Ireland. The 

 tubs are filled with water, but the bottom is covered by a thick layer 

 of soil, and in the soil a few species of water-plants thrive, chiefly 

 the common water-grass, Qlyceria aquaUca. The tubs are covered 

 with wire-gauze to prevent the beetles from escaping. 



Now the Dytiscus possesses a small apparatus capable of piercing 

 the tissues of the water-plants, and each time this borer makes a hole 

 in the water-plant one egg is deposited. In my tubs the lapponicus 

 chose the w\ater-grass as the receptiicle for its eggs. In its native 

 home this grass does not grow, the only water-plants being a common 

 rush, a species of juncus, and the club rush eleocharis, both possessing 

 round stems. Now, the grass possesses a round stem surrounded by 

 leaves, each leaf consisting of a long sheathing base and a free lamina 

 or blade. The sheath is keeled, and in every case the mother-beetle 

 pierced the leaf-sheath, and always in the line of the keel, depositing 

 the egg in the tissues of the sheath, and this shows the pecuhar 



