HYDRANGEA-HYDROMETRID^I. 



monograph upon this genus in the Entomological 

 Magazine. 



HYDRANGEA (Linnaeus). A genus of deci- 

 duous shrubs from North America, but the greatest 

 favourite of the genus is the //. /tortensis, introduced 

 into our gardens from China about 1 788. They 

 belong to the tenth class of Liniuvus, and to the 

 natural order >' One of the peculiarities of 



the Chinese hydrangea is its change of colour of the 

 flowers. In common soil they are pink : but, if kept 

 lor a season or two in peat earth, they become blue. 

 HYDROCAMPA (Latreille). A genus of Lepi- 

 dopterous insects, belonging to the section Xoctitnia, 

 or moths and family /' iving the spiral tongue 



distinct, but differing from Rotiis and the other genera 

 belongi unity by the aquatic habits of 



the larva, (whence the generic name signifying: water- 

 caterpillars) and by the structure of the insect in this 

 state enabling it to reside in such a situation. We 

 know scarcely any circumstance more interesting in 

 /al physiology than that a small assemblage of 



like the present, should be so completely 

 modified in their preparatory structure as to be able 

 to reside in an element which would be certain death 

 to the eau-rpillar* of every other lejn'dopterous insect. 

 In the larva - < feed upon the leaves of 



aquatic plants, such as pond weed, potamogeton, &C. ; 

 and Reaumur has given us an account of the proceed- 



ne of these insects, observed by him in the Hois 

 tin Boulogne, on the under surface of the floating 

 leaves of the last-named plant, and inhabiting a little 

 tnmeable nest, formed out of the leaves of the same 

 plant with considerable mechanical nicety. Piercing 

 the leaf with its jaws and gradually gnawing a curved 

 line, it I norsel of the leaf of the size and 



shape adapted to its wants, which it at first slightly 

 - I ken threads to the under surface of the 

 main-leaf, leaving intervals between them through 

 which it may protrude its head. The piece already 

 .-del for a second piece, which it 



eurately to the former with silk, forming an 

 >val. but within which it introduces its body, retain- 

 meaus of the fleshy lec;s al the 

 binder part of its body, and which it carries about 

 with it from pi.. . using its fore legs, which 



with its head it thrusts out of the aperture left at one 

 Jnd. When, however, it would form a cocoon, in 

 \\w\\ to undergo its transformations, it uses but a 



.'ce, w Inch it attaches more firmly than before. 

 t* under surface bcinsr applied to the under sin face of 



a leaf, on account of the under side of the 

 cat' being concave, by which means a hollow cell is 



-!. although the ire firmly united. 



kVithin this tent it then spins a regidar silken cocoon, 

 \hieh is. of course, secure from the water, being de- 

 ended by its outer leat'v covering ; and in this posi- 

 ion it is soon transformed to a chrysalis, appearing 

 igaiu only when it has become a perfect insect. The 

 aterpillar is of a loin: and fleshy form, its sides being 

 urnished with several lon^r and slender filaments, late- 



.iclied to each segment, and which are em- 



vternal gills for imbibing air from the 



xater. The : to furnished with three pairs 



laced on the three basal joints of 



he abdomen. These spiracles art- of a totally ditt'e- 



ent construction from the gills of the larva 1 , being 



:iy for respiring air ; for the caterpillar 



i as the power not only of rendering its cocoon water- 



>roof, but also of forming it without any water being 



809 



introduced. Still, as if proving that the transition 

 from a watery to an aerial mode of respiration was 

 not yet effected, De Geer, who studied the insects 

 with great care, ascertained that it was absolutely 

 necessary that the cocoons should be kept under 

 water, as the chrysalides died on being removed into 

 the open air. When the time of its last transforma- 

 tion is arrived, the moth, still with its wings unfolded. 

 emerges from its cocoon, creeps up the stems of 

 the plant, and appears in the air, in which alone it can 

 now live. There are several British species of these 

 moths, to which, from the elegant markings of their 

 wings, collectors have given the names of China 

 marks. Some of them are sufficiently common, and 

 m iv be found during the summer months upon aquatic 

 plants. The type of the genus is the Phal<Etia Pota- 

 monota of Linnteus. 



HYDROCHARIDE.E. a small natural order 

 of plants, comprising as yet only four genera, viz., Val- 

 tisneria, Hydrocharis, D<i>n<isoniiii,&nA Stratiotcs, which 

 are all aquatics. The lilyfrog-bit, Ihidrocharis, and the 

 water-soldier, Stratiotcs, with the interesting I'attis- 

 ncria and Damasonium, form collectively the order as 

 above. They are distinguished from each other, as 

 will be seen by the generic characters given under 

 their names respectively. 



HYDROCHARIS (LinunM> A British aquatic 

 herb, commonly called frog-bit or bite : class D'uvcia, 

 and natural order Hi/droctiaridecE. Generic charac- 

 ter : flowers Diivcious, calyx of three sepals, bracteate, 

 and coloured. Petals three, inversely egg-shaped. 

 Stamens triple, inserted on the abortive style; stig- 

 mas three, filiform, united to the inside of the stamen*. 

 Anthers roundish, bursting all round. In the female 

 flowers, the styles are six. two-parted, with abortive 

 filaments. Capsule six-celled, and many seeded. 

 This plant is often met with in wet ditches. 



HYDROCOR1SA ( Latreille). A primary sec- 

 tion of hemipterous insects, comprising such sp 

 as reside in the water, and which differ from the < 

 corisa, or land-biiirs, by having the antenna- minute 

 and inserted beneath the eyes. They are predaceous 

 in their habits, feeding upon other insects, which they 

 seize by means of their fore legs, which serve as 

 claws, the extremities folding upon the basal por- 

 tions. The section comprises two families, the 

 pidce or w ater-scorpions, so named from the chiliferous 

 structure of the fore legs ; and the Notonectidee, or 

 boat-flies, so named from the boat-like form of the 

 body and the oar-like structure of the hind 1 



HYDROCOTTLB (LinnausX A genus of aqua- 

 tic herbs, occurring in many parts of the world. One 

 is common in Britain, and known by the name of 

 pennywort. The genus is only interesting to bota- 

 nists, by whom it is placed in Umbcllij. 



liynROLEACE.E. A natnral'order of plants, 

 containing a single genus only, of which there are two 

 species. They are little elegant plants with blue 

 flowers, chiefly distinguished from Conroli-ulaccic and 

 Polci)ionacf<.c',\n the flowers having two styles, as well 

 as in the two-valved capsules. The leaves are alter- 

 nate and simple, entire or lobed, and without stipules. 



HYDROMETRIDiE (Leach). A family of 

 hemipterous insects, belonging to the section Hcic- 

 -n, and sub-section (rYoivrafl, and affording an 

 instance of the great difficulty attending the natural 

 classification of groups in natural history. From the 

 structure of the antenna 1 and proboscis, these insects 

 are united with the land-bugs ; but in their habits 



