in support of an assertion of Aristotle. 501 



Cap. iv. This chapter treats expressly and almost exclusively 

 of the Testacea^ and in it many animals of the group are men- 

 tioned or alluded to; but the visual organs are not even named, 

 except indeed in the description of the Kafx/v/ov, which, the author 

 says, partakes of the nature both of the MaAaxtcrTfaxa and the 

 Or^Mtiih^fjix. : the eyes of this animal, which is evidently a Pagu- 

 ruSy he particularly mentions.* 



In the eighth chapter of the same book, occupied by an ac- 

 count of the senses and their organs as possessed in general by the 

 various primary groups of the Animal Kingdom, the Testacea are 

 adverted to in these terms : " De visu et auditu quanquam nihil 

 certi manifestique habemus, ungues (S^X^vej) tamen ad strepitum 

 se subtrahere, inferiusque subsidere cernuntur, quoties ferramen- 

 tum sentiunt admoveri. Exiguo namque extant, reliquo autem 

 toto corpore perinde ac in cubili, occuluntur. Pectines (KtiW) 

 quoque admoto digito dehiscunt, mox comprimunt se ut cer- 

 nentes."+ 



We will now proceed to the inquiry as to how far the implied 

 assertion of the Father of Zoology in the first quotation given 

 above, that the Testacea are devoid of eyes, and which the parti- 

 culars respecting certain bivalves subsequently related, cannot, I 

 think, be considered as contradicting, agrees with the statements 

 ef modern science. 



Of the six classes into which the il/o^/wsca have been divided by 

 Cuvier, we may at once dismiss from the inquiry the first, or the 

 Cephalopoda', and that without having recourse to the distinction 

 between those animals and the true Mollusca, which has been 

 established by IVlr. W.S. JVIacleay ; for we have seen that Aristotle 

 himself distinguishes them from his O'rpxy.i^epfji.x. The animals con- 

 stituting three of the remaining classes, — the Acephalfi, compre- 

 hending the greater part of the Bivalves, the Brachiopoda, com- 

 prising the remainder of them, and the Cirripeda, M'hich in- 

 clude the various species of Lepas, Linn., — are all well known to 

 be devoid of eyes. The only classes, then, with which we are at 

 present concerned, are the Pteropoda and the Gasteropoda. 



* Ibid. p. 821. t Ibid. p. 828. 



