. The Cambridge natural history. Zoology. ADEPHAGA—WATER-BEETLES 21 I. degrees, the legs in the genera Bytiscus and Hyclro'porus being but slender, while those of CyMster are so broad and powerful, that a single stroke propels the Insect for a considerable distance. The wing-cases fit perfectly to the body, except at the tip, so as to form an air-tight space between themselves and the back of the Insect; this space is utilised as a reservoir for air. When the Bytiscus feels the necessity for air it rises to the surface and exposes the tip of the body exactly at the level of the water, separati
. The Cambridge natural history. Zoology. ADEPHAGA—WATER-BEETLES 21 I. degrees, the legs in the genera Bytiscus and Hyclro'porus being but slender, while those of CyMster are so broad and powerful, that a single stroke propels the Insect for a considerable distance. The wing-cases fit perfectly to the body, except at the tip, so as to form an air-tight space between themselves and the back of the Insect; this space is utilised as a reservoir for air. When the Bytiscus feels the necessity for air it rises to the surface and exposes the tip of the body exactly at the level of the water, separating at the same time the abdomen from the wing-cases so as to open a broad chink at the spot where the parts were, during the Insect's submersion, so well held together as to be air- and water - tight. The ter- minal two pairs of spiracles are much enlarged, and by curving the abdomen the beetle brings them into con- tact with the atmosphere; respiration is effected by this means as well as by the store of air carried about under the wing - cases. The air that enters the space between the elytra and body is shut in there when the Insect closes the chink and again dives beneath the water. The enlargement of the terminal stigmata in Bytiscus is exceptional, and in forms more highly organised in other respects, such as Cijbister, these spiracles remain minute; the »presumption being that in this case respiration is carried on almost entirely by means of the supply the Insect carries in the space between the elytra and the base of the abdomen.^ The structure of the front foot of the male Bytiscus, and of many other water-beetles, is highly remarkable; the foot being dilated to form a palette or saucer, covered beneath by sucker-like structures of great delicacy and beauty ; by the aid of these the male is enabled to retain a position on the female for many hours, or even days, together. Lowne has shown that the 1 For many particulars as to respiration of Dytiscus, and peculiariti
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
