A D E S M A C E A A D H E S I O N. 



articulations, without pores or cells, as hard as coral, 

 and separated from eaeh other by disks or plates of a 

 horny, fibrous, and flexible substance. The expansion, 

 as has been already observed, is stiff and brittle. Its 

 hardness is equal to that of many of the madrepores, 

 and superior to that of most of the millepores ; the 

 cells or pores are very numerous, placed in short 

 curved lines, or dispersed on both surfaces ; ,v.ll those 

 found on the same side appear to communicate with 

 each other by very thin perforated divisions; and the 

 polypi of the two surfaces appear to be insulated by 

 means of a diaphragm, which is very thick, and parallel 

 to the plane of the two surfaces, dividing the polypidom 

 into two lamina? of an equal thickness. 



The colour of the adeona is an iron-grey, some- 

 times of a deep hue; they occasionally attain a foot in 

 height, arid are abundantly found in Australia. Six 

 species are known. 



ADESMACEA. A family of shells, forming the 

 third class of Acephalophora, established by De Blain- 

 ville, in his System of Malacology. It includes the 

 genera Pkolas, Tcredina, Teredo, Fistuluna, and Sep~ 

 taria. All the species of these genera possess the 

 extraordinary faculty of piercing hard bodies, such as 

 marble, wood, &c. A more detailed account of the 

 habits of each will be found in their respective alpha- 

 betical arrangements. 



ADHESION literally means the property which 

 substances have of " sticking together" after having 

 once been separated, or of growing up united as one 

 when, under other circumstances, they grow sepa- 

 rately. The term is used in the arts and in the 

 sciences of dead matter, and there it denotes the 

 adhering together of different substances or different 

 masses ; and differs from cohesion, by means of which 

 the parts of one mass are held together. 



In Natural History the word adhesion has a signifi- 

 cation somewhat different, namely, that the substances 

 do not merely adhere together, but grow together, and 

 become as it were one. In this sense it is applied to 

 natural substances in their living state only ; but it 

 applies equally to animal and vegetable substances, 

 and some of their most remarkable properties depend 

 upon it. 



There are some remarkable cases of adhesion that 

 take place in animals, chiefly in the mammalia, 

 though occasionally in some of the other classes, while 

 they are in the uterus or other maternal envelope. 

 These chiefly consist of the union of two subjects, 

 neither of which is (mite perfect : at times both 

 nearly in equal perfection, as was the case with the 

 Siamese twins, some time ago exhibited in London ; 

 and at other times with the one so little developed, 

 that it seems merely a fragment stuck upon the other 

 as an additional limb, a finger, or a thumb. These 

 formations, to which the name of MONSTERS has been 

 given, form one of the most obscure portions of the 

 branch of physiology, of which we know the least, 

 inasmuch as we have no analogous knowledge upon 

 which we can ground even a plausible conjecture, 

 neither is it probable that such knowledge will ever 

 be obtained. There are natural causes for their 

 monstrosity no doubt, as well as there are for all the 

 phenomena of nature ; but we know not in what di- 

 rection these causes may lie ; and, consequently, any 

 speculation concerning them would, of necessity, be 

 extremely doubtful. If one lamb in a thousand be 

 dropped with five legs, we need not puzzle ourselves 

 about the cause of that, till we have found out " why " 



the nine hundred and ninety-nine have only four legs 

 each. The number in the one case satisfies our 

 curiosity, and the rarity of the other awakens it, but 

 we are equally ignorant of the " why " in both. 



Vegetable adhesions are turned to more account 

 than animal ones ; and we are enabled to pursue the 

 subject a little farther, though when we come to 

 adhesions in their primary formation, we get upon 

 ground which is hardly less slippery. In vege- 

 tables we can carry the adhesions, at least in some 

 of the natural families, to different species, and 

 perhaps to the Whole genus, or, in some instances, 

 to the whole natural family or order. The cases 

 in which we can most easily effect this, are those 

 in which there is a power of forming lateral buds, 

 or buds in the bark, or rather in the living cam- 

 bium ; but there are other cases in which it is dif- 

 ficult, if not impossible, to form an adhesion, even 

 of the parts of the same individual, however recent 

 the division may be. There is no action for the 

 repair of waste in those parts of a plant which have 

 passed thuir season of vegetation ; and therefore we 

 could no more expect a power of adhesion in them, 

 than in the salts of lime in the bones or in the appen- 

 dages to the skins of animals. It is at the living 

 surface of the wood in the exogenous, or the living 

 centre of the endogenous plant, where we alone ever 

 find action ; and as there is productive action there 

 only while the cambium of the plant is in a state of 

 granulation, there can be no healing or union by the 

 first intention in a plant. It is true, that the action 

 in perennial stems is not confined to the mere surface 

 at which the new substance accumulates during the 

 growth of the seasou ; for there must be some organi- 

 sation or apparatus for the elaboration of that sub- 

 stance ; and thus the action of the vegetable may be 

 said to linger a little longer in the external layers of 

 the alburnum or sapwood, and the inner layers of the 

 bark, according to the habit of the species. But 

 when these structures are once consolidated, they do 

 not unite even by a process similar to granulation ; 

 and hence the "internal shakes," which are found 

 in the boles of trees, in those countries where 

 they are exposed to the effects of violent winds. 

 Hence also the union by grafting must be by meai.s 

 of a mere twig ; and if that twig is inserted in the 

 hard wood only, it is sure to wither ; unless that mould 

 decomposes and forms a soil in which it can take 

 root. Even with the living surfaces of the scion 

 and the stock in contact, there must be a sort of 

 overlaying or overlapping of those surfaces ; for 

 though they are adapted ever so neatly to each other, 

 they will not adhere upon a perfectly horizontal sec- 

 tion. 



The parts of growing plants are often subject to 

 the same kind of adhesion which takes place in ani- 

 mals, when the parts are deprived of the epidermis, 

 and held in contact. This often occurs naturally in 

 trees which bud in the bark, and gives them very 

 fantastic appearances : and it is not confined to 

 deciduous trees, but is met with in some of the 

 coniferaa, such as the yew, the old hollow trunks of 

 which are often covered by a network of younger 

 parts, which adhere and again separate over it in the 

 most singular manner, entwined like open rustic 

 work, after the old part has mouldered away. Fruits 

 and leaves often adhere in the same manner; and 

 indeed, in many species, there are no two similar 

 purt^ of the living surface that will not adhere if they 



