VERMES. 



eryllalHne, is no where fo diftiiiftly feen as iu the eye of the 

 cuttle-fi/h. They form a large zone or diaphragm, in the 

 aperture of which the cryftalliiie is truly encafed. A deep 

 circular furrow paffes completely round the cryftalline, and 

 divides it into two unequal hemifpheres. The cihary pro- 

 ceffes penetrate into this furrow, where they are fo firmly 

 frxed, that they cannot be removed without being torn. 

 The procefs is not formed of projefting laminae, but of a 

 continued membrane, the two furfaces of which are marked 

 by a circle, confifting of a vaft number of fine radiated ftriiE, 

 which prefent a very agreeable fpeftacle. 



The fepJK have glandular bodies between the fclerotica 

 aad the choroid ; but none between the latter and the tunica 

 Ruyfchiana. The feparation of thefe two membranes is even 

 fometimes difficult ; the choroides is more thick, foft, and 

 vafcular, the Ruyfchiana thin and dry. There is no tape- 

 turn, all the eye being hned internally by a deep purple pig- 

 ment. The pupil is (haped hke a kidney. 



After the numerous optic filaments have perforated the 

 choroid, they are confounded in 3 fingle membrane, the 

 retina. 



The cryftalline divides eafily into two hemifpheres, the 

 limits of which are marked externally by a deep fun-ow : 

 each hemifphere confifts of a number of concentric cups, 

 compofed of radiated fibres. 



As the conical fclerotic of the fepis is attached to the bot- 

 tom of the orbit, the glandular bodies, which ferve to fupport 

 the globe, are fituated, not between it and the orbit, but 

 between it and the choroid. The part fixed to the edge of 

 the optic hole is pointed ; it preferves therefore fome degree 

 of mobility. There are onlvtwo fmall mufcles, one fuperior 

 and an interior, the head being fuppoled upwards. 



Ttlie fepisE and other mollufca, which have not the eyes at 

 the extremity of their tentaciila, have no eye-lid ; the flcin 

 covers the eye, as in ferpents and eels. But the flugs, fnails, 

 &c. have an organization, which is far more comphcated, 

 and much better calculated for the proteftion of their eye. 

 This organ is fituated at the extremity of a flefhy tube, 

 called a horn or tentaculum, which may be drawn completely 

 within the head, and protruded by a motion fimilar to the 

 evolution of the finger of a glove. We have already de- 

 fcribed the mufcles that draw the fnail into its fheU. The 

 particular mufcle of tlie eye is attached at the external edge 

 of each of thefe mufcles : this mufcle penetrates to the in- 

 fide of the horn, to the extremity of which it is fixed. 

 When it contrafts, therefore, but ftill more when alTilled by 

 the contraftion of the great mufcle of the body, it draws 

 the extremity of the horn inwardly, in a manner which re- 

 fenibles the turning in of a ftocking. The annular fibres, 

 which encircle the horn throughout the whole of its length, 

 unfold the internal part by fucceffive contraftions, and thus 

 bring back the eye to its external pofition. In the Aug, the 

 retradors of the eyes are fimply attached to the flefhy raafs 

 which forms the foot. In the inferior horns or tentacula, 

 which have no eyes, the mechanifm is alfo the fame. 



The gafteropodous mollufca are the only order, among 

 the animals we are now confidering, that polTefles an organ 

 of hearing. No animals placed below thefe in the fcale of 

 being are known to poffefs fuch an organ, although there 

 are proofs of the faculty in many. The ear of the fepias is 

 very fimple ; it is entirely concealed in the body of the an- 

 nular cartilage, which ferves as the bafe of the great tenta- 

 cula, or feet of thefe animals. Towards the back of the head 

 there is an eminence of the cartilaginous ring, unperforated, 

 and covered by the thick integument of the animal. The 

 membrane of the labyrinth contained in this part is a fimple 

 purfe of an oval or roundilh form, containing a clear fluid. 



In the common cuttle-fifh (fepia officinalis), it has internally 

 feveral conical eminences, difpofed in an irregular manner : 

 thefe eminences are wanting in the other fpecies. In the pulp 

 which fills the membrane there is a fmall body fufpended, 

 which is ofTeous in the cuttle-fifh properly fo called, and like 

 ftarch in the oftopus. In the fepia officinalis it referables a 

 fmall fhell. See Scarpa de Auditu et Olfadlu. 



Organ of Touch — We do not eafily dillinguifh all tlie 

 parts which compofe the integuments o' vertebral animals, 

 in thofe that have no vertebrse : fome of the ftrata are more 

 diflinft, others lefs fo : there are alfo fome fpecies in which 

 we do not find the whole of them. Of the animals we are 

 now confidering, different orders dwell in different fituations, 

 and are expofed to very different external circumflances : 

 there are correfponding variations in their outward coverings. 

 Some live in the inteftines of other animals, the mucous 

 fluids of which fufificiently proteft them ; others are enclofed 

 in calcareous or flony habitations, neceffary to enfure them 

 from the agitations of the waves, and from the furrounding 

 hard bodies. Others have a hard integument, covered fome- 

 times with fpines. 



There is an epidermis in invertebral animals : thofe whicii 

 live in water have it commonly mucous ; it is of a very dif- 

 ferent thicknefs in the feveral fpecies. It is nearly the fame 

 in the cephalopoda as in fiflies. In the naked gafteropoda 

 it very much refembles that of falamanders and frogs. 



There is an epidermis on the (hells of moft teflacea. In 

 the land kind, as the fnails, it is a dry pellicle, very eafily 

 detached, when the fhell is, after the death of the animal, 

 expofed to the aftion of the atmofphere, or plunged into 

 boiling water. In the mufcles, both of frefh and fait water, 

 and in other bivalves, we obferve a fimilar epidermis, which 

 envelopes the fhell externally. This epidermis is always 

 wanting on the furface of the projefting parts, on which the 

 animal draws its fhell along the fand, becaufe it is there 

 worn off. In fome fpecies of fhells, the epidermis is thick 

 and vifcous, and on this account it has been named fea-cloth. 

 Th's is very remarkable in feveral fpecies of the genus area 

 of Liimseus ; and to exprefs this pecuharity, he has called 

 one of them pilofa. 



In all the teflacea, the epidermis which envelopes the 

 fhell is continued to produce the pellicle, which covers the 

 animal, and it produces the fame change as that which is 

 prolonged within the body of vertebral animals. It is thin 

 and mucous on all the parts which are not expofed to the 

 aftion of the ambient fluid. In the fpecies of gafteropoda, 

 however, whoffe fhell is concealed under the fkin, and does 

 not ferve for defence, the epidermis does not change its 

 tiature. We have examples of this in fome fpecies of 

 aplyfia and fcyllea, as well as in the animal which produces 

 the fhell, called by Linnaus helix halyotoidea (figaretof 

 Lamarck). 



Worms have a diftinft cuticle, which is eafily feparated 

 from the (liin in the earth-worm, when it has been immerfed 

 for a few hours in fpirits of wine, or macerated fome days in 

 water : it is a pretty folid pellicle, which may be removed 

 in a fingle piece. In the fipunculus faccatus this epidermis 

 is even entirely feparated from the body, which is uncon- 

 nefted and floating within it, as if it were inclofed in a fac. 

 Leeches and fome other worms have the cuticle mucous, 

 hke that of the gafteropodous mollufca. 



It is very difficult to afcertain the nature of the epidermis 

 in zoophytes, or even to difcover whether it exifts in fome 

 of them. The fea-ftars (afteriasl, the urchins (echinus), 

 and the acliniae, appear to poffefs it. The medufa? are co- 

 vered with a pelhcle, but fo thin and tranfparent that it 

 cannot be fuppofed to confift of ftrata. The other zoo- 

 phytes, 



