V POLYMORPHA HYDROPHILIDAE 2 I 7 



tliree j^fM'ts, a hasal part of one or two elongate joints, an inter- 

 mediate part of two or more small joints, and an apical part of 

 larger (or at any rate broader) joints, v^hich are2)t(.hescent, the others 

 being hare. Outer lobe of maxillae iisucdly complex, but not at 

 all p(dpiform, maxillary palpi often very long ; the parts of the 

 labium much concecded behind the mentum, the labial palpi very 

 widely separated. Hind coxae extending the width of the 

 body, short, the lamina interior small in comparison with the 

 lamina exterior. Abdomen of Jire risible segments. The Hydro- 

 philidae are an extensive family of beetles, nnattractive in colours 

 and appearance, and much neglected by collectors. A large part 

 of the family live in water, though most of them have only 

 feeble powers of aquatic locomotion, and the beetles appear 

 chiefly to devote their attention to economising the stock of air 

 each individual carries about. The best known forms of the 

 family are the species of Hydrophilus. They are, however, very 

 exceptional in many respects, and are far more active and pre- 

 daceous than most of the other forms. Much has been written 

 about Hydrophilus piiceus, one of the largest of British beetles. 

 This Insect breathes in a most peculiar manner : the spiracles 

 are placed near bands of delicate pubescence, forming tracts that 

 extend the whole length of the body, and in this particular 

 species cover most of the under surface of the body ; these 

 velvety tracts retain a coating of air even when the Insect is 

 submerged and moves quickly through the water. It would 

 appear rather difficult to invent a mechanism to supply these 

 tracts with fresh air without the Insect leaving the water ; but 

 nevertheless such a mechanism is provided by the antennae of 

 the beetle, the terminal joints of which form a pubescent scoop, 

 made by some longer hairs into a funnel sufficiently large to 

 convey a bviljble of air. The Insect therefore rises to the sur- 

 face, and by means of the antennae, which it exposes to the air, 

 obtains a supply with which it surrounds a large part of its 

 body ; for, according to Miall, it carries a supply on its back, 

 under the elytra, as well as on its ventral surface. From the 

 writer's own observations, made many years ago, he inclines to 

 the opinion that the way in which the Hydrophilus uses the 

 antennae to obtain air varies somewhat according to circumstances. 

 Many of the members of the sub-family Hydrophilides con- 

 struct egg-cocoons. In the case of Hydrophilus piceus, the boat- 



