H Y A 



[ 120 ] 



H Y D 



and divided at their summit into three 

 lobes. When its wings, or sails, are 

 unfolded, it moves with great velocity on 

 the surface of the sea. The Pteropods, 

 both from the beautiful colouring of their 

 filmy wings, and from their number and 

 symmetry, are better entitled to the ap- 

 pellation of the butterflies of the ocean, 

 than the escalop shells, which have 

 sometimes been so called. Rev. W. 

 Kirby. 



HY'ALINE. (from hyalus, Lat. VCL\QQ , Gr.) 

 Transparent. 



HY'ALITE. (waXoc, Gr.) A yellowish or 

 greyish variety of uncleavable quartz or 

 opal. It exhibits the usual appearance 

 of a concretion, and differs but little 

 from calcedony, except in possessing a 

 vitreous lustre, and sometimes a loose 

 texture. It is found in secondary trap j 

 rocks ; it occurs ingrains, filaments, and 

 rhomboidal masses. It is infusible before 

 the blow-pipe. It is nearly all silica, its 

 component parts being silica 92'00, wa- 

 ter 6-33. 



HYBER'NACLE. (hibernacula, Lat.) 



1. The winter dwelling or residence of 

 animals. 



2. That part of the plant which defends 

 the embryo from injuries arising from 

 frost. 



HYBE'RNAL. (hibernus, Lat.) Belonging 



to the winter. 

 HY'BERNATE. To pass the winter in places 



protected from the cold, as some animals 



burrow in the 'earth, others in the trunks 



of trees, &c. &c. 

 HYBERNA'TION. 



1. The passing of the winter season in a 

 situation protected from cold. 



2. In many animals a general suspension 

 of the actions of life, extending even to 

 the vital functions of respiration and cir- 

 culation, takes place during the winter 

 months, constituting what is termed hy- 

 bernation. 



HY'B-RID. (v/3pie, Gr. hybrida, Lat. hy- 

 bride, Fr. ) Mongrel ; a term applied 

 both to plants and animals, when of a 

 cross-breed. 



HY'BODONT. (from w/36f, and dens, Lat.) 

 A sub-family of sharks, according to the 

 arrangement of M. Agassiz. They seem 

 to have begun with the coal formation, 

 to have continued throughout the oolitic 

 deposition, and to have ceased at the 

 beginning of the chalk formation. The 

 teeth of this sub-family possess characters 

 intermediate between the blunt crushing 

 teeth of cestracionts, and the sharp cut- 

 ting teeth of squaloids. 



HY'BODUS. A genus of fishes that pre- 

 vailed throughout the oolitic period. It 

 is well remarked by Prof. Buckland, "not 

 a single genus of all that are found in 



the oolitic series exist at the present 

 time." 



HYDA'TID. (vSarlg, Gr. hydatide, Fr.) 

 An order of internal worms. In hydatids 

 there has not been discovered any vascular 

 system. Hydatids, so frequently found 

 in the liver and other parts of the body 

 in mammalia, have been considered by 

 some as animals, consisting merely of a 

 stomach ; by others, as a matrix, or 

 womb, from something like young hyda- 

 tids being frequently found adhering to 

 their inner side. Hydatids immersed in 

 warm water, immediately after being ob- 

 tained from a living animal, are observed 

 to have a contractile power, but they 

 have no external opening ; they are pel- 

 lucid spherical bodies, of different sizes 

 and kinds. Each consists of two coats, 

 the inner of which is extremely delicate. 

 They do not possess any visible blood- 

 vessels, though the sac containing them 

 has abundance of vessels, nerves, &c. 

 derived from those of the organ with 

 which it is connected. Hydatids ought 

 not to be confounded with watery vesi- 

 cles, connected occasionally with the 

 kidney, &c. which are not enclosed in 

 cysts, have no small hydatids adhering to 

 their inner surface, and want contrac- 

 tility. There are many genera. 



HY'DRATE. (from i'wp, Gr.) A chemi- 

 cal compound in definite proportions of 

 a solid body with water, still retaining a 

 solid form. It must, however, be borne 

 in mind that when water in combination 

 with other bodies contributes (as in crys- 

 tallized bodies) to their regular form and 

 transparency, it is then termed water of 

 crystallization. The hydrates are nume- 

 rous, as hydrate of alumine, baryta, co- 

 balt, copper, lime, magnesia, potassa, 

 soda, &c. &c. 



HY'DRATED. Mixed with water, but re- 

 taining its solid form. 



HYDRAU'IIC. "^ (vdpavXlg, Gr. hydrauli- 



HYDRAU'LICAL. S> cus, Lat. hydraulique, 



HYDRAU'LICK. J Fr. idraulico, It.) Re- 

 lating to the conveyance of water through 

 pipes. The siphuncle of the nautilus, 

 ammonite, belemnite, &c. forms a very 

 beautiful and complete hydraulic appa- 

 ratus. 



HY'DRAULICS. The science of the motion 

 of fluids, and the construction of all kinds 

 of instruments and machines relating 

 thereto. 



HY'DROGEN. (from vo>p and ysvi'aw, Gr.) 

 One of the fifty-five simple, or elementary 

 bodies. Inflammable air, proved by Ca- 

 vendish to be the basis of water, from 

 which circumstance it has obtained its 

 name. It can be obtained only from 

 water. Hydrogen is colourless, and has 

 commonly a slight odour of garlic ; it is 



