Notes, iv. 5. 223 



102). So also a considerable division of air-breathing gasteropods is inoperculate. 

 The land-snails, however, close their aperture during hybernation by a layer of hardened 

 mucus soinetimes strengthened by carbonate of lime. This A. had noticed. For he 

 speaks {H. A. viii, 13, 15) of the land-snails as having a superficial operculum during 

 hybernation. The op'erculum when present is so "from the very birth," and the use 

 of the expression shows that A. had attendedto the development of the gasteropods. 



The operculum of a gasteropod can scarcely be considered to be the homologue of. 

 the second valve of ' a . lamellibranchiate mollusc, for it is developed from the foot, hot 

 from the mantle. Adanson, however., and more recently Mr. Gray, thought such to be 

 the cage' {Woodward's Manual, p. 47). Though not homologous, to the valve, it is 

 however analogous to it j that is, it serves the same purpose, namely, to protect the 

 animal when retracted into the shell. 



32. There does not seem sufficient evidence to decide what molluscs exactly are meant. 

 'This is the short description given {,H. A. iv. 4) : " The Nerites has a large smooth 

 round shell, in form like that of the whelk. * But its mecon is red, not black as is that of 

 thewhelk.T * . 



36. The Bivalves in reality have no odontophore or tongue. 



34. This passage with others shows that the Hist. Animalium and the lost treatises on 

 Anatomy were illustrated. • Cuvier indeed {Hist. d. Sc. 1. 141) says the latter contained 

 coloured illustrations. I can find no authority for this statement. There is none in 

 the 28 passages referring to the i.vaTOfiai collected by Heitz ( Verlor. ^chr. des Arist. p. 70). 



36. By Tethya are undoubtedly meant Ascidians, as the description Jiere . and in the 

 Hist. .<4«. (iv. 6) shows, and I have therefore so rendered it. A. includes both Echini 

 and Ascidia among the Testacea ; though they are, as he says, very different from the 

 three main groups of these animals. That he should so have classed Echini was but 

 natural.; for they would appear to him^ to have all . the characters which distinguish his 

 Testacea, viz. a hard brittle covering "(which however is not really external), a mouth 

 turned downwards, a stomach, intestine, vent, mecon, and so forth. But that he should 

 have so classed 'the Ascidians, that have no hard shell, is more remarkable. He had, 

 however, perceived that the extfemal covering of the Ascidians is in reality a. shell. 

 *' Their whole body, he says, is hidden in a shell. This shell is something intermediate 

 between skin and shell proper, so that it cuts like hard* leather." In the Museum 

 Catalogue (CoU. of Surg. i. 266) it is said that, " Mr. Hunter, who perceived the relations 

 subsisting between Ascidia and Salpa, and knew the true analogy of their external 

 covering, proposed to distinguish them as a distinct group of Mollusks under the term 

 'soft-shelled,' which more truly accords with their real nature than 'shell-less,' as they 

 have subsequently been designated by Cuvier." 



36. The jaws of Echinus vdth the five teeth form a conical mass, which is still described 

 by writers as "the lantern of Aristotle," in reference to a comparison mjcde va. H.A. iv.' 

 5, 8. . . • . ' 



37. The flesh-like piece is said in the Hist. An. (iv. 5, 5,) to be. in place of a 

 tongue, and to occupy the centre, df the cavity formed by the teeth. As the Echin.us has. 

 no tongue, the pharyngeal portion of the oesophagus must be meant. 



38. The oesophagus of Echinus terminates in a much wider tube, which is continued to 

 the anus without any distinct separation into stomach and intestine. This gastro-intestinal 

 tube is attached, by what may be called a mesentery, to the inner surface of the shell, 

 in such a manner as to form loops or festoons, five in each of its two coils ; and it is to 

 this appearance of subdivision that A. alludes. This is" plain not only from the careful 

 way in which he here guards himself from saying that there are actually a number of 



