HYD 



HYD 



HYDROPHILUS, in natural history,^ 

 genus of insects of the order Coleoptera. 

 Antennae clavate, the club perfoliate ; 

 feelers four, filiform ; the hind leg's are 

 formed for shimming, fringed on the in- 

 ner side, and nearly unarmed with claws. 

 The insects of this genus, like those of the 

 DYTISCUS, which see, are inhabitants of 

 ponds and stagnant waters, where they 

 swim with much dexterity, turning round 

 with great velocity ; they fly abroad by 

 night in search of other waters. The males 

 are distinguished from the females, by 

 having a horny concave flap or shield on 

 the fore legs, near the setting on of the 

 feet ; the hind legs are peculiarly fitted 

 for their aquatic situation, being furnish- 

 ed on the inner side with a series of long 

 and close-set filaments, resembling a fin, 

 by which they are enabled to swim with 

 great ease. The larva remain about two 

 years and a half before they change into 

 pupae, forming a convenient cell, and se- 

 creting themselves in some bank. They 

 are very voracious, and destructive to the 

 more tender aquatic insects, worms, and 

 young fish, which they seize with their 

 forked jaws, and destroy, by sucking out 

 their juice. There are upwards of thirty 

 species. The principal European species 

 is the H. piceus, water-clock. The fe- 

 male of this species affords an example of 

 a faculty, which seems to be exercised by 

 no other insect of this order, -viz. that of 

 spinning a kind of web, or flattish circu- 

 lar case of silk, which it leaves floating on 

 the water, and in which it deposits its 

 eggs. This case, says Dr. Shaw, is termi- 

 nated, on its upper surface, by a length- 

 ened conical process, resembling a horn, 



of a brown colour, and of a much stronger 

 nature than the case itself, which is white. 

 The larvae, as soon as hatched, make their 

 escape from the envelopement of the 

 case, and commit themselves to the wa- 

 ter. 



HYDROPHOBIA, in medicine, aa 

 aversion or dread of water; a terrible 

 symptom of the rabies canini. See ME- 

 DICINE. 



HYDROPHYLAX, in botany, a genus 

 of the Tetrandria Monogynia class and or- 

 der. Natural order of Rubiaceae, Jussieu. 

 Essential character : calyx four-parted ; 

 corolla funnel-form ; fruit ancipital, one- 

 seeded. There is only one species, viz. 

 H. maritima, found in driving sand, on 

 the sea-shore, near Guduluhr in the East 

 Indies. 



HYDROPHYLLUM, in botany, ivater- 

 leaf t a genus of the, Pentandria Monogy- 

 nia class and order. Natural order of Bor- 

 ragineae, Jussieu. Essential character : 

 corolla bell-shaped, having five longitu- 

 dinal melliferous streaks on the inside; 

 stigma bifid; capsule globular, two-valv- 

 ed. There are two species, viz. H. vir- 

 ginicum, Virginian water-leaf; and H. 

 canadense, Canadian water-leaf. 



HYDROSCOPE, an instrument ancient- 

 ly used for the measuring of time. The 

 hydroscope was a kind of water-clock, 

 consisting of a cylindrical tube, conical at 

 bottom : the cylinder was graduated, or 

 marked out with divisions, to which the 

 top of the water, becoming successively 

 contiguous, as it trickled out at the ver- 

 tex of the cone, pointed out the hour. 



HYDROSTATICAL balance, a kind of 

 balance contrived for the easy and exact 



