VERMES. 



phytes, as the polypes, &c. have a mucous furface, tlie 

 ioftncfs of which prevents us from diftinguifhing any mem- 

 brane. 



Mofi moUufca have a rete mucofum below the epidermis. 

 In the cephalopoda it is moft commonly of a blue or red 

 colour ; but it forms a very thin layer. That of the gaf- 

 teropoda varies confidcrably, as we may obferve particularly 

 in the Aug. It is thick and vifcous ; but difiblves com- 

 pletely, in water. In fituation, the fliell is analogous to rete 

 mucofum. It is found immediately under t)ie epidermis, 

 and, when fome of the calcareous part is removed, it is a 

 kind of cruft without any apparent organization, and not a 

 membrane. It is produced by fucccltive llrata. Finally, 

 it is coloured, and its fliades arc infinitely various. 



The rete mucofum is to be found in a fmall number only 

 of zoophytes : and it cannot even be feparated from tlie 

 (kin, as in the afteria; and actiniae. 



It appears to be confounded with the calcareous fiiell, 

 which forms the habitation of feveral other genera. This 

 may be obferved in fome fpecies of echini and coralhiies ; and 

 in the ceratophytes, and a number of lithophytes. 



Nothing at all approaching to the appearance of nervous 

 papilla can be feen m white-blooded animals. In the cepha- 

 lopodous mollufca fome nervous filaments may be feen in 

 the fmall globules, which feem glandular, and which cover 

 the {l:in. In other mollufca, fome nervous filaments may 

 be traced into the fubilance of the flcin ; but they cannot 

 be feen to form papillae. 



No real cutis is to be obferved in the invertebral animals, 

 excepting the cuttle-fifh and the other cephalopoda. It is 

 applied almoll immediately to the mufcles, by means of a 

 very denfe cellular fubilance : it is of a very coriaceous na- 

 ture, and not eafily lacerated. Its fibres are very (lender. 



In the other invertebral animals, there is no part which 

 can be compared to the cutis. There is, indeed, a pelhcle 

 under. the (liell of the cruftacea, but it is fine, tranfparent, 

 and has very little confidence. The ftin cad off by the 

 larva: of infefts in moulting, is of the fame nature and thick- 

 nefs as that below it, and which is dcitined to fuccecd it. 

 Even the envelop of certain chryfalides, as thofe of the 

 lepidoptcra and diptera, cannot be regarded as cutis : it is 

 rather a kind of horny epidermis. In the perfcft ftate, 

 there is no part of tlie teguments of infects that can be 

 compared to the cutis. The fame obfervatiou applies to 

 the worms and zoophytes. 



In the invertebral animals, that' have foft bodies, almoft 

 all the mufcles may be confidercd as cutaneous ; for the 

 greater number are attached to the (kin. But as they are 

 alfo employed in progredion, they are dcfcribcd among the 

 organs of motion. 



Befides the (]<in in general, which is an univerfal organ of 

 touch iri man, and the red-blooded claffes, there are parti- 

 cular organs poffefiing a much more acute power of dif- 

 cerning the tangible properties of bodies, aiid at the fame 

 lime fo conftnicted as to admit of eafier application to their 

 furface. The fingers exemplify this. It may be doubted 

 whether the invertebral claffes have any parts calculated to 

 perform fiich an office ; and we nather think that they have 

 not. Some, iiowcver, regard the tentacula as organs of 

 touch, and confider them analogous to the antenna; of in- 

 fe£ls, or to the fingers of man and the qnadrumana. 



We have already defcribed the tentacula of the cephalo- 

 podous mollufca, under the head of Organs of Motion. 

 They obvioudy ferve for fcizing their prey ; but whether 

 they enjoy any fenfc of touch is extremely doubtful. 



The horns of the fnail have been defcribed in tlie account 

 of the eye. Thofe of the other genera among the gallcro- 



poda do not differ, except that they are incapable of that 

 motion by which the former are retracted and protruded like 

 the finger of a glove. They have mufcular fibres, which may 

 be contracted or relaxed. 



Tentacula are found in many invertebral animals ; but 

 they are not fo univerfal as the antennx among infefts. 

 They are fituated on the head ; often at the opening of the 

 mouth, as in the doris ; above it, as in the flug; or round it, 

 as in the terebella. Several fpecies have fimilar appendices 

 round the cloak. Such are the rimpcts, the genus halyotis, 

 &c. Among the acephala, the greater part are provided 

 with thefe appendices, and fome have them in great num- 

 bers. In the fpecies which have the cloak completely open 

 they are placed around it, and particularly towards the 

 anus : this may be obferved in oyllers, mufcles, &c. In 

 thofe in which the cloak opens by a tube only, the ap- 

 pendices are attached to the circumference of its orifice. 

 Such are the genera venus, cardium, &c. The tube itfelf 

 furnifhes thefe animals with an excellent inftrument of 

 touch. The fle(hy and ciliated arms of'the genera lingula 

 and terebratula are equally proper for this employment ; 

 but thofe of the anatifa are very inferior, in confequeuce of 

 their horny fubftancc. 



Cirri are found in feveral fpecies of worms ; and they 

 fometimes appear to be formed of different articulations, tike 

 the antenna: of iufefts. Nen-es proceed into thofe of the 

 aphrodita and nereis. There are none in the lumbricns 

 and leech ; but their place is fupplied in the latter by the 

 two difks which terminate their bodies. Their mimber 

 varies : generally there are two, the flug has four, the 

 cuttle-fifli eight, the peiinatula forty to fixty or more. Many 

 varieties of form are alfo obferved, and defcribed by writers 

 in natural liiftory. Tlie tentacula of the polypes are faid to 

 be hollow, and to communicate with the ftomach. Fine 

 hairs are obferved in them, by means of the microfcope ; 

 they alfo poffefs numerous knots, which probably are of 

 fervice in fixing them on animals which they feize for prey. 

 Throughout the invertebral claffes, we find thefe inftru- 

 ments chiefly ufed for feiiing the creatures on which the 

 animal lives. Tlie tiibularia, hydra, brachyonus, vorticella, 

 &:c. throw the water into motion by means of their arms. 

 \Vlien any thing on which they can prey comes near, they 

 inltantly feizc and convey it to the mouth. Trembley ob- 

 ferved, that the tubularia fultana (polypes a bouquet) gave 

 a rotatory motion to the water, and thus condufted the prey 

 to their arms. Olivi obferved, that the aftinix and polypes 

 (hydra) perceived their prey at a diftance, put the water in 

 motion, and thus brought it within the fphere of their arms. 

 Speaking of thefe organs, Cuvicr fays, " the anus, the 

 tufts and the flowers of feveral zoophytes (polypi, La- 

 marck) ; the innumerable tentacula of the fea-llars, urchins 

 and adtiniae, and the complicated branches of the medufae, 

 are excellent organs of touch." 



Of the infenfible parts, covering the (kin, very little re- 

 mains to be faid ; we have already defcribed the formation 

 of the (liell, and have made fome further remarks on it in 

 fpeaking of the (l(in. 



Many of the vermes clafs have the body furni(hed with 

 bunches of hairs, which are fometimes (liff and ix-traAile, 

 and ferve for feet, as we have pointed out in the genera 

 nereis, terebella, lumbricus, &c. In the aphrodita, there 

 are, befides thefe brilllcs employed in progreffioii, an infinite 

 munbcr of other hairs, which are long, flexible, and of a 

 changeable fea-green colour ; there is alfo a tomentous 

 felt-like fubftancc, covering the branchii, through which 

 the water is llrained. 



Organ of Smclling.-'Thi fatvdty of Imell is connected in 



all 



