EYES AND HORNS. 77 



made the mistake of calling the great nerve of the tentacle, and 

 which is really the nerve of touch, the optic nerve ; and so his 

 statements were all put aside together. Professer Owen speaks 

 veiy confidently on the subject, and in the Museum of the Eoyal 

 College of Surgeons he has one of those wonderful preparations 

 with which he has enriched that noble collection, in which the 

 tentacles of Helix pomat la are extended so as to show the eye at 

 the side of each extremity. In this position the eyes, the pro- 

 fessor very justly observes, although destitute of appropriate 

 muscles, have the advantage of all the mobility with, which the 

 tentacles themselves are endowed ; while, by the admirable con 

 struction of the tentacles, they are securely defended from ex- 

 ternal injury. 



It would be a difficult matter, probably, to find a person any- 

 where who had never seen a Snail draw in its horns on their 

 being touched ; but how many, we should like to know, have 

 ever closely watched the Snail's manner of doing it? Those 

 little horns, as the learned professor above mentioned properly 

 says, are " admirable " contrivances, and the way in which they 

 are so nimbly drawn in is not a little curious. The thing is easily 

 seen, and any schoolboy may ascertain how it is done, the next 

 time he stops a Snail in his travels across the footpath, and 

 admonishes him, in the words of the old doggerel, "to shut up 

 his house and go away home." The secret is, that the tentacle 

 is a hollow tube, and in being withdrawn, it is simply inverted 

 and retracted like the finger of a tight glove ; only that the 

 extremity, with the eye-spot upon it, is always the first part to 

 disappear. The manner of il. is best seen, perhaps, when, after 

 the tentacle has been withdrawn, it is again protruded ; as you 

 can then readily discern that the organ is lengthened, not by 

 being pushed out from its base, but by gradually unfolding itself, 

 or being everted at the extremity till the clubbed point appears, 

 and the tentacle is fully extended. One cannot but admire the 

 wisdom which thus gives the little Mollusc such a ready and 

 effectual means of defending its rather oddly located visual 

 organs. We speak of the wonderful contrivances connected 

 with the human eye, but surely there is something here that is 

 not much less wonderful. 



If we may rely on the experiments of Swammerdam, the Snail 

 tribe have the sense of smell, as well as that of sight. The late 



