GASTEROPODES. 273 



The main ducts terminate in the thickness of the side, at a consider- 

 able distance from the head. 



A very great diiference prevails both in the colour and in the general 

 aspect of the specimens of this animal. Leaden grey, or a ferruginous 

 hue, in general predominates ; and such, in as far as I have had an 

 opportunity of observing, are always specimens of the largest size. One, 

 extending about three inches, of transcendent beauty, was universally 

 pure white, unless the central tuft of the corniculum, tending to the olive. 

 It was taken near the Bass Rock. Another, extending towards four 

 inches, was of a beautiful transparent primrose-yellow. The branchiae 

 were very transparent ; the colour of all the rest uniform, rather more 

 vivid than primrose-yellow ; and the aspect of the animal so beautiful 

 and peculiar, that it seemed to me, at first sight, as if a new animal. 



Homberg's Doris is rarely white ; but specimens an inch long occur 

 sometimes several at the same time. No peculiarity is concomitant on 

 the colour. The sole is always dingy white. Some adults are brown 

 as copper, whereas smaller specimens are commonly grey, or almost 

 white. 



Cuvier says he has assured himself of the presence of eyes. If so, 

 they are probably deep seated, as he speaks from the result of dissection. 

 Omission to specify the eyes of many of the minor animals, is not the 

 denial of their existence, whether in the Doris or in others. The nature 

 of the parts may oppose their detection. Colour may conceal them in 

 one specimen, contrast may expose them in another. The powers of 

 vision, in a different medium from air, cannot be satisfactorily estimated, 

 without knowing much more of the organs. 



The whole body is susceptible of great alterations. The cornicula 

 may be completely retracted ; and all its three portions are endowed with 

 independent action. The branchiae are susceptible of alternate con- 

 traction and dilatation ; and the entire animal enlarges greatly, when 

 crawling, above its dimensions in repose. In full vigour, and during 

 genial weather, the specimen represented in Plate XXXVIII. figs. 1, 2, 

 extended eight inches, whilst in motion. It seemed too heavy to attempt 

 swimming supine, as done by smaller subjects. It is only under salubrious 



2 M 



