HYDRA. 



I to He cmillrn poaribl* stream how inconceivably 

 rmay indeed be imagined, but there is no thread fin* enough 

 to anil H, mini that the tentaoula of H.J<uca, in tension, can be 

 ((red lo nothing groscer than the scarce visible filaments of the 

 grammar's web. 



The 11*1, though usually found attached, can neverthele** move 

 from place to place, which it doe* cither by gliding with imperceptible 

 duelled on the base, or by stretching out the body and tentaoula to 

 UM utmost, axing the Utter, and then contracting the body toward* 

 UM point of fixture, Innccning at the came time it* hold with the base ; 

 and by reversing these action* it can retrograde. Its ordinary posi- 

 tion ceem* to be pendant, or nearly horizontal, hanging from some 

 floating leaf or weed, or stretching from Its ides. In a glsss of water 

 UM creature will crawl up the aide* of the vessel to the surface and 

 it, sometimes with the base and sometimes with the 

 iownwards; and again it will lay itself horizontally. Its 

 is very alow, and the disposition of the zoopbite is 



evidently sedentary ; but the contraction* ai d mutations of the body 

 are very vivacious, while in seizing and mastering its prey it is sur- 

 prisingly nimble, seizing a worm with a* much eagerness as a cat 

 catches a mouse. It enjoys light, and expands more freely under its 

 ta^Mi. ; hence we generally find the Hytlr.i near the surface and in 

 shallow water. The Hydra are very voracious, feeding only on living 

 animal*. In confinement however Trembley found they might be 

 fed on minced veal, fish, or beef and mutton. They wiU sustain 

 long facU with no other change than a paler colour indicates. Small 

 crustacean*, and insects seem to form a favourite food. 

 M* two polyp* will seize upon the same worm, and most 

 i* H then to witness the struggle that ensues, sometimes 

 resulting in the swallowing of the weaker polyp by the stronger, 

 which however is soon disgorged with no other loss than bis dinner. 

 This i* the more curious when contrasted with the fate of the worms 

 on which they feed. No sooner are they seized than tbey evince 

 every symptom of painful suffering, but their contortions are merely 

 momentary, and a certain death suddenly follows their capture. How 

 this efleet i* produced i* still a matter of conjecture. Worms are in 

 ordinary circumstances most tenacious of life, and hence one is in- 

 clined to suppose that there must be something poisonous in tbe 

 Hydra fgrup. To the t'ntomottraca the touch is not equally fatal, their 

 shell evidently protecting them from the poisonous secretion. The 

 JJfdn is chiefly celebrated on account of its manner of propagation. 

 It i* like soophytea in general, monoecious, and every individual pos- 

 eeecec the power of continuing and multiplying its race, principally 

 however by the process of subdivision. During the summer season 

 a Urge tubercle arises on the surface, which lengthening and enlarging 

 every hour, in a day or two develops in regular succession and in 

 successive pain a series of teutacula, and become* in all respects 

 except in size similar to its parent It remains attached for some time, 

 and grows and feeds, and contract* and expands r.f'.er the fashion of 

 ite parent, until it is at length thrown off by a process of exfoliation 

 or Nougbing. They develop with great rapidity in warm weather, 

 and aometime* the young ones themselves breed others, and they again 

 a third or fourth generation before they become separated from tbe 

 original parent Trembley found that an individual of //. yruea 

 produced 45 young one* in two months. In autumn tbe Hydra gene- 

 rate* by internal oviform geminules, which extrude from the body, 

 and lie during the winter in a quiescent state, and are stimulated to 

 evolution only by the returning warmth of the spring. Few obser- 

 vations have been made on these ova, so that their structure, source, 

 manner of escape, and condition are scarcely known. 



These are the modes in which the Hydra naturally multiplies it* 

 kind, but it can be increased by artificial sections of the body in the 

 came manner that a perennial plant can by shoots or slips. If the 

 body be halved in any direction each half in a short time grows to a 

 perfect Hydra; if it u cut into four or eight or even minced into forty 

 pieeea, each continue* alive, and develops a new animal which is 

 Waif capable of being multiplied in the same extraordinary manner. 

 If the section i* made lengthwise ao a* to divide the body into two or 

 ore slip* connected merely by the tail, tbey are speedily reunited 

 into a perfect whole, or if the piece* are kept asunder each will become 

 a perfect polyp. If the tentacuU are cut away, new one* an 

 quickly produced, and the lopt-off parts are not long without a new 

 body. When a piece is cut out of the body tbe wound speedily heals, 

 and a* if excited by the stimulus of the knife, young polyps sprout 

 from the wound more abundantly; when a polyp is introduced by 

 the tail into another body, the two unite and form one individual, and 

 when a bead i* lopt off, it may safely be ingrafted on the body of any 

 other which may chance to want one. And the creature suffers 

 nothing itself by all thcee apparently cruel operations; for before the 

 lap** of many minute* the upper half of a crocs Action will expand its 

 UaUcuU and catch prey as usual, and the two portions of a longitudinal 

 division will afur an hour or two take food and retain it A polyp cut 

 tnniemly in three part* require* four or five day* in summer 

 and longer in cold weather for the middle piece to produce a head 

 andaUiLaadttMtailparttogeta body and head, which they do in 

 pretty much the same time. And what U .till more extraordinary, 

 Hyp* produced in this manner grow much larger and are far more 

 prolific in the way of their natural increase than those which were 



HYDRANOEACEA in 



never cut When such things were first announced, when to a little 

 worm the attribute* of angelic beings were assigned, and the wild 

 fictions of antiquity realised, it is not wonderful that the vulgar 

 disbelieved, when naturalists, familiar with all the mirncles of the 

 insect world, were amazed and wist not what to do. 



Tbe following are British specie* of this genus: 



//. riridu (Polypes Verds of Trembley), is of a grass-preen colour. 

 Tbe body cylindrical or insensibly narrowed downwards ; tentacula 

 6 to 10, shorter than the body. It is commonly found in ponds and 

 still waters. Tbe polyps of this species differ from tbe following, 

 not only in colour, but likewise in their arms, which are much 

 shorter in proportion to their bodies, capable of but little extension, 

 and narrower at the root than the extremity, which is contrary to 

 the other species. Their arms were so short they could not clasp 

 round a very small and slender worm, but seemed to pinch it fast 

 till they' could master and devour it, which they did with as much 

 greediness as any. It was first observed in England in the spring of 

 1743 by a Mr. Ducane of Essex. It appears to be a hardy animal, 

 and U easily kept for a length of time in a phial of water. 



//. rulyarii is of an orange-brown or yellowish colour, body 

 cylindrical, teutacula 7 to 12, as long or longer than the body. It is 

 found in weedy ponds and slowly-running waters. This does not 

 exceed 11. viridii in size, which it resembles also in its habits and 

 form. It is always of an orange-brown or red colour, the intensity 

 of the tint depending on the nature of tbe food, or the state of tbe 

 creature's repletion. Every part of the body is generative of young, 

 which may frequently be Been hanging from the parent at the same 

 time in different stages of their growth. 



11. allcnuata is of a light oil-green colour, the body attenuated 

 below, with pale tentacula longer than itself. It is found in ponds, 

 and in Yetholm Lough, Roxburghshire. This is a larger animal than 

 11, ruiyarii, and comparatively rare, less sensible to external impres- 

 sions, and of a more graceful form. Its colour is a pale olive-green, 

 with paler tentacula, which are considerably longer than tbe body, 

 and bang like silken threads in the water, waving to and fro without 

 assuming that regular circular disposition which they commonly do 

 in //. viriilui. Dr. Johnston says he has not observed more than one 

 young at a time, which pullulated from near tbe middle of tbe body, 

 and after this has attained a certain growth tbe polyp has tbe 

 appearance of being dichotomously divided. 



11. oli [/act is (Polypes a Long Bras of Trembley) is brown or griseous ; 

 inferior half of the body suddenly attenuated ; tentacula several times 

 longer than tbe body. It is found in still waters in England, rare. 

 In a pond at Hackney; and in a pond at Cranmoro, near Belfast, 

 September 1812. The tails of these are long, slender, and transparent, 

 and when placed under the microscope a long straight canal may bo 

 seen passing from the body or stomach to an opening at the end 

 thereof ; these are rather lighter coloured than 11. vulgarit, and have 

 seldom more than 6 or 8 arms, but those capable of great extension. 

 It may be worth while to call attention to tbe remarkable resemblance 

 of the Hydra fusca to the Oucullantu cirratiu of Mullcr, which is 

 an intestinal worm. 



(Johnston, Hittory of Britith Zoophylei ; Landsborough, Popular 

 Ilittory of British Zoopliytet ; Trembley, Memoires pour tervir a 

 fHutuirt d'un Genre de Polypes d~au douce, tbe Hague, 1743 ; Baker 

 Natural Hittory of the Polype.) 



HYDRACHNA. [TRACUKA.RIA.] 



HYDRACTINIA. [HYDROUU.] 



HYDKAl.KS. [ENDOOENS.] 



HYDRANGEA. [HYDRANUEACEJE.] 



HYDRANQEACE^E, Hydrangeadt, a natural order of Exogenous 

 Plants consisting of shrubs, with perfectly opposite simple leaves, 

 smooth cr downy, with simple bnirs, destitute of stipules, sometimes 

 creeping and rooting like ivy. Flowers usually in cymes; those in 

 tbe centre male, tbe marginal often sterile, and furnished with larger 

 petals than tbe others. Calyx adhering more or less to the ovary, 

 4- or 6-toothed. Petals 4 or 6, inserted within tbe edge of- the calyx, 

 deciduous. Stamens 8 or 12, in two rows, inserted in the orifice of 

 the calyx, distinct, deciduous. Anthers oblong or roundish, pollen 

 with three longitudinal furrows. Ovary more or less adherent to the 

 calyx, consisting of from 2 to 6 carpels, adhering by their sides, and 

 forming an incompletely 2- or 6-celled cavity ; placenta: diatiuct from 

 each other, but touching with many anatropal ascending or horizontal 

 ovules ; styles as many as tbe carpels, perfectly distinct, diverging, 

 with simple reniform stigmas. Fruit a capsule crowned by the 

 permanent diverging etyles, 2- or 6-celled, with a number of minute 

 seeds, sometimes indefinite, sometimes few, in consequence of the 

 abortion of a part of tbe ovules. Testa thin, membranous, netted, 

 occasionally expanded into a wing. Embryo ortbotropal in the axis 

 of a small quantity of fleshy albumen. The relationship between 

 Hydrangead* and Saxifrages is admitted by all systematists, who 

 have in general united them in tha same order. Lindley places this 

 order between Saxifragaeea and Cunoniaceas, and near Pliiladelphaceae 

 and Caprifolvueas. It differs from Hentloviacac mainly in its 

 indefinite seeds, small quantity of albumen, and constant tendency 

 to produce a superior ovary. Out of the species hitherto discovered, 

 all of which inhabit the temperate parts of Asia and America, two 

 only belong to the southern hemisphere, and twenty-three or about 



