I 82 



Marvels of the Universe 



Let us now examine the means of locomotion, the mechanism which propels tiiis boat-shaped 

 beetle through the water. The two front pairs of legs, especially in the female, are used for crawling 

 among weeds, for seizing prey, and for anchoring the insect when it desires to remain in one position 

 beneath the surface. In the male the front pair of limbs is specially modified to enable him to 

 seize and retain the female. One of the joints is flattened and furnished with sucker-like discs and 

 cupules, well shown in the figure on page 183. But the larger hind limbs have undergone great 

 modification and are, in effect, a couple of powerful paddles. By a peculiar keel-like prolongation 

 of the chest, they are set far back below the centre of the insect, and their arrangement and 

 attachment enable them to be brought at right-angles to the body, thus providing for a strong, 

 wide sweep. i\Ioreover, the whole form of what we may term the foot — the five-jointed terminal 

 portion of the leg — has been flattened and clothed with stiff hairs until it is transformed into a per- 

 fect reciprocating oar-blade. These 

 paddles are operated by powerful 

 muscles. They generally strike the 

 water simultaneously, driving the 

 beetle rapidly forward in a straight 

 line ; but they are also capable of 

 being used singly for the purpose of 

 turning in a confined space, just as 

 an expert sculler will use one oar to 

 manoeuvre his skiff. 



While the Diving Beetle is thus 

 admirably fitted for progress through 

 the water, its habits are by no means 

 exclusively aquatic. True, its per- 

 formance when afoot amounts to 

 little more than an undignified 

 scuttle, but its wings are large and 

 well developed, and the beetle fre- 

 quently makes long aerial excursions, 

 especially at night, travelling from 

 one pond or stream to another. It 

 is, indeed, a wonderful colonizer, and 

 there can be few suitable sheets of 

 water, from one end of the kingdom 

 to the other, which it has not made 

 its own. This beetle has been known 

 to pitch precipitately upon the roof of a greenhouse, probably mistaking the glint of the glass in the 

 moonlight for water. Moreover, when imprisoned in an aquarium, it is liable to effect its escape 

 and turn up in the kitchen or parlour, much to the consternation of the lady of the house. 



The manner in which the Diving Beetle takes in its supply of oxygen is very remarkable. In 

 order fully to appreciate it we must first fix in our mind the facts that insects have no lungs 

 and that they do not breathe through their mouths. They take in air through holes in their sides, 

 known as spiracles, each spiracle being guarded by a sort of quickset hedge of stift' hairs, which 

 serves to keep out dust and dirt. Just within each spiracle, or breathing-hole, there is an ingenious 

 little valve which opens and closes periodically by a muscular contrivance. The air which enters 

 through the open valve is conveyed direct to every part of the body through a system of minute 

 tubes, the final ramifications of which are so delicate that they penetrate the most distant extremities 

 of the body. These air-tubes are soft and within them run spirally-coiled threads of hard material 



J'lwlo !.(;] yiarohl ISasliii. 



THE "SPIRACLE- OF THE WATER BEETLE. 



The Diving Beetle has no lungs, nor does he breathe through his mouth. 

 He is supplied, however, with air-holes in his side and upon his back, each 

 of which is guarded by a network of stiff hairs from the intrusion of any 

 dirt or dust. 



