GASTEROPODA. 



389 



of the pylorus. A similar disposition occurs 

 in Faguwlta (fig. 189, /, ti ). 



Fig. 189. 



In Scylltfa the liver (fig. 187, d) is divided 

 into six small and detached round masses, the 

 excretory ducts of which open above the point 

 where the oesophagus joins the singularly armed 

 gizzard (c). The liver of Aplysia is very large 

 and forms three principal masses, among which 

 are seen the convolutions of the intestine. The 

 biliary canals are very wide and open into the 

 third stomach near the aperture communicating 

 with the rudimentary pancreas (Jig. 188, e). 

 In Testacella Haliotoidea there are two livers 

 perfectly distinct from each other, and from 

 each arises a proper duct, which opens sepa- 

 rately into the commencement of the intestine 

 near its origin. Onchidinm furnishes us with 

 a still more curious arrangement, being pro- 

 vided with three distinct livers, pouring their 

 secretions by separate canals into different parts 

 of the alimentary tube. Each portion perfectly 

 resembles the others in external appearance, 

 and in structure as well as in the nature of 

 their respective secretions. The excretory canal 

 which proceeds from the largest mass enters 

 the oesophagus, discharging itself near to its 

 cardiac termination ; the duct of the second 

 terminates near the same point, whilst the bile 

 produced by the third is poured into the 

 gizzard itself. The insertion of the two former 

 above the gizzard would seem intended for the 

 same purpose as the abundant secretion which 

 is poured into the ventriculus succenturiatus of 

 Birds, namely, to moisten the food before its in- 

 troduction into the gizzard ; it is, however, sin- 

 gular to find the biliary fluid employed for this 

 purpose ; nor is the insertion of the third duct 

 into the first of the three stomachs of this animal 

 less extraordinary, a similar arrangement occur- 



ring only in a few fishes, as in the Diodon 

 Mola. 



The liver of Doris is very large, and not 

 only is the bile which it secretes discharged by 

 large and numerous ducts into the stomach, so 

 wide, indeed, that it is difficult to conceive 

 how the food is prevented from entering them, 

 but moreover the liver furnishes a second duct 

 of large calibre, which opens externally in the 

 vicinity of the anus. A part of the bile in this 

 case is evidently excrementitious, as there is 

 no doubt that the second canal takes its origin 

 from the substance of the liver. " This," says 

 Cuvier speaking upon this subject, " is the 

 first instance of the kind which I have met 

 with, and the fact was sufficiently singular to 

 make me hesitate long and examine the matter 

 with all possible precaution before admitting 

 it. It is only by one supposition that it can 

 be explained otherwise, namely, that the lobes 

 of two different glands are so interwoven that 

 they are not to be distinguished from each 

 other, one portion producing bile used in the 

 process of digestion, and the other secreting a 

 fluid which escapes by the canal in question." 

 Before its termination externally, the secondary 

 duct communicates by a short canal with a 

 lateral receptacle, which forms a kind of gall- 

 bladder, having its lining membrane much 

 corrugated and its walls apparently muscular ; 

 this is probably a reservoir for the excremen- 

 titious fluid, in which it may be retained until 

 the animal feels its discharge necessary. There 

 is reason to suspect that the fluid thus furnished 

 is a colouring matter, used as a means of de- 

 fence, and expelled like the ink of the cuttle-fish 

 on the approach of danger, but the matter is 

 undecided. 



The bile is in all cases produced from arte- 

 rial blood, and the liver is provided with but 

 one system of veins answering to the hepatic. 



Organs of respiration. The respiratory or- 

 gans of the Gasteropoda are found to be con- 

 structed upon very various principles, adapted 

 to the medium which they inhabit, or the pecu- 

 liar exigencies of the individuals composing 

 each order. Nevertheless in different groups 

 allied by the generalities of their organization, 

 the respiratory system is, in most instances, 

 found to be constructed upon the same plan, 

 and this circumstance more than any other has 

 rendered the position and nature of the respira- 

 tory organs the most eligible basis of classifica- 

 t.on. On looking over the table which we 

 have given at the commencement of this ar- 

 ticle, the reader will perceive at once that the 

 names by which the different orders are desig- 

 nated indicate the general disposition of the 

 pulmonary or branchial appendages, and we 

 shall therefore follow the arrangement there 

 adopted in considering more minutely the pe- 

 culiarities belonging to each. 



The first or Nudibranchiate order is distin- 

 guished by having the breathing apparatus per- 

 fectly exposed to the influence of the surround- 

 ing medium, which in all the genera belonging 

 to this division is the water of the ocean ; the 

 branchiae constantly assume the shape of arbo- 

 rescent tufts, placed in different situations upon 

 the dorsal aspect of the animal. In Doris (see 



