their Organs of Respiration* ' 24-7 



completely out of the water, that they seem to merit the ap- 

 pellation of amphibious. Of these the Patellae and the Lit- 

 torinae (Turbo Lin.) are remarkable examples. Our common 

 species of the latter genus (Turbo littoreus and Merita litto- 

 ralis of British conchologists) seem indeed to prefer spots 

 where they can be covered only at high water, and I have 

 seen myriads of them, when young, clustered in hollows of 

 rocks that were many feet above the highest tides. Still, their 

 respiratory organs are, as they ever have been, branchial ; nor 

 does it seem easy, on the Lamarckian hypothesis, to account 

 for their non-improvability : why these shell-fish, so fond of 

 air, have not acquired, by their residence in it, the lungs of 

 the snail, and betaken themselves to the land ; why their shells 

 have not become lighter, to enable them to move with more 

 alacrity ; and why their eyes have not risen to a higher eleva- 

 tion than the base of the tentacula, that they might scan the 

 landscape, and avoid its perils. The habits of the Chitonidae 

 are similar to those of the Littorinae. " Those animals," 

 says the Rev. Mr. Guilding, " frequent the rocks and stones of 

 the sea-coast, and are distributed nearly over the whole globe. 

 Many of the species are constantly under water, while others 

 ascend above low or even high water mark, spending the day 

 exposed to the hottest sun, or selecting a resting-place which 

 is only occasionally moistened by the rude and restless surf. 

 In Chitonellus and Cryptoc6nchus there are certain minute 

 organs on the zone, which bear a strong resemblance to the 

 spiracula of the annulose animals. From their habit of quit- 

 ting the watery element, like many of the Turbinidae, I once 

 supposed that the organs for the aeration of the circulating 

 fluid might be of a compound nature (pulmdno-branchiati). 

 It is, however, far more probable (as in the case of some 

 crustaceous genera which I am now investigating) that this 

 process is capable of a diurnal or a temporary interruption, 

 or that the branchiae, so long as they are kept moist, and 

 shielded from atmospheric influence, may perform their func- 

 tions, though much more slowly." (Zool. Journ., vol. v. p. 29.) 

 I shall continue this subject in my next. 



G. J. 

 April 23. 



r 4 



