614 



MOLLUSC A. 



Mollusca. opening. The intestine makes several folds, chiefly in 



'""""Y"^*' the liver, before it reaches the anus. The salivary 



glands reach to the extremity of the gullet. The liver 



is divided into five lobes, which gives rise to two ducts 



that open into the pylorus. 



The circulating system consists of two vente cava?, 

 which give out numerous branches to the pulmonary 

 cavity. The aerated blood is conveyed by several 

 ducts to a simple menibranaceous systemic auricle. 

 Between the auricle and ventricle there are two valves. 

 The ventricle is more muscular than the auricle. The 

 arteries, which take iheir rise from a single aorta, are 

 characterised by a peculiar opacity, and whiteness of 

 colour, as if they were filled with milk. 



The organ of viscosity nearly encircles the pericar- 

 dium. It cons:sts of regularly pictinated plates. Its 

 excretory canal terminates at the pulmonary cavity. 



Tile organs of generation consist, in the female parts, 

 of an ovnrium, oviduct, and, uterus ; and in the male 

 of a testicle, vas deferens, and penis, together with 

 the pedunculated vesicle ; and as common to both 

 the sexual organs there is a cavity opening externally, 

 in which, by separate orifices, the uterus, penis, and 

 vesicle, terminate. 



The species of this genus have hitherto been chiefly 

 characterised by the shape and colours of the body ; the 

 latter, however, is liable to such great variation, that 

 it is difficult to determine the number of species which 

 are natives of Britain. The structure of the shield, 

 and the relative position of the pulmonary cavity, join- 

 ed with the markings of the body, ought to be resort- 

 ed to ; and could a knowledge of the internal structure 

 be likewise obtained, we might then hope to be able 

 to bestow on the species permanent marks of distinc- 

 tion. 



Although the terrestrial gasteropoda may be consi- 

 dered as phytivorous, it is now known that the larger 

 species of this genus likewise feed on the common 

 earth worm, as has been observed by Mr. Power, 

 (Lhm. Trans, vol. ix. p 323.) None of these species 

 are used in this country as food. 



II. PARMACELLA. The animals of this genus are 

 distinguished by the position of the shield, which is 

 placed on the back, near the middle of the body, and 

 contains, at its caudal extremity, an open subspiral tes- 

 taceous plate. Underneath the shield is the pulmonaiy 

 cavity. 



The only species of this genus yet known was found 

 by M. Olivier in Mesopotamia. The genus was insti- 

 tuted by M. Cuvier, and the species denominated P. 

 olivieri. Along the back, from the shield to the head, 

 are three grooves ; the medial one is double. From the 

 dissections of Cuvier it appears, that the internal struc- 

 ture of this species bears a close resemblance to that of 

 the slugs. The most remarkable difference is in the 

 two conical appendages of the common sexual cavity, 

 by which they approach the Helices. 



Testaceiia. 1 1 1- TESTACELLA. The shield in this genus is placed 

 on the posterior extremity of the body, and, conse- 

 quently, the anus and pulmonary cavity are nearly ter- 

 minal. These are protected by an open subspiral tes- 

 taceous plate. The foot extends on each side beyond 

 the body. From the manner in which the blood is ae- 

 rated, the auricle and ventricle are placed longitudinal- 

 ly, the latter being anterior. 



The T. haleotoidea, described and figured in the 

 Histoire Nalurelle des Molhisques Terrestres et Fluvia- 

 iiles de la Franct, par M. Draparnaud, p. 121. tab. xi. 

 figs. 1214-, is the only species which has been dis- 



Farmacel- 

 la. 



tinctly ascertained. It lives in the soil, and pursues Mo!iwri. 

 and feeds on the common earth worm. ^ ~~~i~~** 



TRIBE II. The animals of this tribe were formerly 

 included in the genera Helix and Turbo of Linnaeus. 

 The shells are spiral, and more or less turbinated. They 

 are covered with a cuticle, which, in some cases appears 

 in the form of ridges or hairs, The following genera 

 have been established : 



I. HELIX. Snail In this genus the animals have Hclii. 

 four tentacula, as in the Limax, with eyes at the tips of 

 the superior ones. The aperture of the shell, which is 

 somewhat lunulated, is as wide as it is long. 



The internal structure of the snails very nearly re- 

 sembles that of the slugs. The shield, however, has a 

 thickened margin in front, by which the shell is form- 

 ed, and the centre of the shield is as it were ruptured, 

 giving vent to the liver and organs of generation. These 

 occupy the cavity of the shell towards its tip, and the 

 mouth is filled with the foot, body, and head. The 

 animal is attached to the pillar of the shell by a com- 

 plicated muscle, which shifts its place with the growth 

 of the animal. The mouth is furnished above, with 

 a thin arched corneous mandible, notched on the 

 edges. 



The circumstances in which the snails differ from 

 the slugs, are chiefly observable in the organs of gene- 

 ration. The vagina, previous to entering the common 

 sexual cavity, is joined by the canal of the vesicle, and 

 by two canals, each proceeding from a bundle of mul 

 tifid vesicles. Each bundle consists of a stem, which 

 is the canal, and numerous branches with blunt termi. 

 nations. These canals pour forth a thin milky fluid, 

 whose use is unknown. 



Connected with the sexual cavity is the bag in which 

 the darts are produced. The bag itself is muscular, 

 with longitudinal grooves, and a glandular body at the 

 extremity. This glandular body secretes the dart, 

 which is in the form of a lengthened pyramid, consist- 

 ing of calcareous filaments nearly resembling asbestus. 

 Previous to the sexual union, the two snails touch each 

 other repeatedly with the mouth and tentacula, and 

 at last the dart of the one is pushed forth by its 

 muscular bag, and directed against the body of the 

 other, into which it enters, never penetrating through 

 the integuments, and even in many cases falling short 

 of its mark. Whether the use of the dart is merely 

 to stimulate, or whether it is subservient to any 

 other purpose, can scarcely be said to be determi- 

 ned. 



The species of this genus are numerous, and may ad- 

 mit of distribution into several sections, from circum- 

 stances connected with the form of the shell. Without 

 instituting these at present, we shall subjoin a list of 

 the species indigenous to Britain, which belong to this 

 restricted genus: 1. H. pomatia ; 2. virgata; 3. cin- 

 genda; 4. rufescens ; 5. cantiana; 6. hispida; 7. lucida; 

 8. trochiformis ; 9. spinulosa ; 10. caperata ; 11. ra- 

 diata; 12. umbilicata; 13. lapicida; 14.. albella (of Dra- 

 pernaud,) found near St. Andrew's by Mrs. Fleming, 

 Flisk ; 15. ericetorum ; lt>. paludosa ; 17. crystallina 

 (of Draparnaud,) found at Battersea by Dr. Leach; 

 18. aspersa; 19. memoralis; 20. arbustorum; 21. fusca; 

 22. elegans (of Draparnaud), the Trochus terristris of 

 British writers. 



The Searches of Montfort is formed from the Helix 

 scarubicus of Linnaeus. 



II. BULIMUS. The shell furnishes the distinguishing Bulimus. 

 mark in this family. It is turreted, and the mouth is 

 longer than it is broad. The following species are in- 



