BEITISH WATERBUGS. 81 



stationary at the surface, but on the slightest suspicion, a few 

 strolves of their powerful oars drive them instantly far from 

 clanger. The under side of the abdomen, i.e., the deck of the 

 boat, slopes inwards on either side, so that there are two large 

 gutters between the strong central keel and the equally strong 

 outer sides ; these sides and the central keel are bridged over 

 all along by thick layers of coarse, oblique hairs, one layer to 

 each side from the central keel, and one from each side to the 

 keel, thus forming a waterproof upper deck. When the boat- 

 man rises to the surface for air, the apex of the body projects 

 a little out of the water, the air passes along the tunnel each 

 side under the hairs ; along the bottom of the tunnel (or gutter) 

 are six pairs of spiracles into which the air passes. Under 

 water this supply of air is very noticeable, seeming like a mass 

 of mercury. 



The anterior pair of legs is raptorial; the middle pair is used 

 for clinging to stems of weeds, &c., while at rest ; in this position 

 the posterior legs stand out at right angles to the longitudinal 

 axis of the body, this latter pair being long, with the tibiae and 

 tarsi densely ciliate. Their speed through the water can be very 

 great, but on land their gait is very clumsy, their progression 

 being effected by a sort of shufSing hop. They are provided 

 with strong organs of flight, and use them indeed with good 

 results. 



Copulation takes place beneath the surface of the water ; the 

 abdominal segments are telescopic, and the terminal segments 

 are thrust out beyond the apices of the tegmina, so that the 

 spiracles are still protected from the water. The male mounts 

 the female at first in the usual way, but soon after slips down so 

 that the sexes lie almost in the same plane, side by side, the 

 male a little lower ; they swim thus, attached only by the geni- 

 talia, as quickly almost as when separate. 



Observations on the metamorphoses have been made by 

 Pioesel, Eegimbart, Dufour, De Geer, Girard, Bueno, Enock, and 

 myself; while embryological researches have been made by 

 Heymons, Will, Pedaschenko, Pantel, Sinety, and others; at the 

 same time full descriptions and figures of the various stages in 

 this, as in all other British waterbugs, are much needed. 



The ova of N. glauca are oblong, cylindric ; they are usually 

 inserted, for about three-fourths of their length, in incisions 

 made in the stems of rushes, or other aquatic plants, though 

 sometimes they are only lightly affixed thereto, or, in exceptional 

 cases, deposited on the bottom, though possibly ova found 

 scattered promiscuously thus may have originally been so lightly 

 affixed to the stem of some plant that a subsequent jar dislodged 

 them. Piegimbart has b!gured the ova of N. glauca in situ, and 

 he enquires the reason of these insects thus concealing their ova 

 in plants. At first sight, he says, there is reason to suppose 



