36 WHIRLIGIG BEETLES. 



oars; these are rather in the form of paddles. The whole action of 

 the insect in the water, as it performs its gyrations about in the 

 sunshine, is not unlike that of a canoe dexterously propelled by 

 the paddle. Perhaps, if we glance at the construction of the leg 

 of the Dytiscus the difference will be more evident. It is long 

 and narrow, the joints of the tarsus being elongated, the last 

 being produced to a point and fringed with long hairs, so as to 

 present, in the act of swimming, a large surface of resistance to 

 the water ; but owing to these hairs lying close to the leg they pass 

 easily through the water, when it is drawn up preparatory to 

 another stroke, feathering in a very effective and perfect manner. 

 The posterior leg of a Gyrinus (Plate II., Fig. 6) is very short, 

 each part being much widened out, and each joint of the tarsus 

 enormously so on the inner side ; and on the outer side both tibia 

 and tarsus are fringed with long, strong bristles, so that when the 

 leg is extended it presents a very large surface to the water, and 

 yet, by the peculiarity of its construction, can be closed up in a 

 fan-like manner into a very small compass. The intermediate 

 legs are similar, but narrower. 



The Gyrijiida, unlike DytiscidcB, pass the greater portion 

 of their existence on the surface of the water, but they can dive 

 exceedingly well, which they nearly always do when alarmed. 

 They, however, do not remain long under the water, but very soon 

 come up and re-commence their gyrations on the surface. 



The sub-family, Gyrmidie^ contain only two genera : Gyriiius 

 and OredocJiilus. The genus Gynjius contains ten British species; 

 the genus Orectochilus only one, viz., O. villosus. It is smaller 

 and rather different in shape to the true Gyrifii, and instead of 

 being smooth and polished it is hairy. It has also another pecu- 

 liarity, namely — that it hides under leaves, etc., during the day 

 and performs its evolutions on the water by night. The ten 

 species of British Gy7'ini are very difficult to determine : in fact, I 

 think it is almost impossible to make them out by any description, 

 the differences consisting of peculiarities of form such as cannot 

 be expressed in words, although they are evident enough by com- 

 parison when you are sufficiently familiar with the various species. 

 Again : the males and females of some species differ, the 

 females being duller and more punctured than the males. Others 



