146 KEW: THE FACULTY OF FOOD-FINDING IN GASTROPODS. 
I think, in assuming that they possess an additional sense for this 
purpose. The powers of sight with which they are usually accredited, 
it 1s true, cannot avail them much; for, though doubtless able to 
distinguish different degrees of light,’ it is doubtful whether they 
possess the power of vision as we understand it, and almost certainly 
they are incapable of distinguishing objects at a distance. But 
in all probability, as most will agree, the creatures find their food by 
sense 
ust e 
that in order to explain o observed facts it would have to be ‘a very 
exquisite sense, beyond any delicacy we can comprehend; but as 
Dr. Sochaczewer has observed, we must not compare the senses of 
invertebrates too critically with those of vertebrates ;? we, Darwin 
held, inherit the power of smell in an enfeebled condition,* and 
in animals as far removed as the gastropoda. Unfortunately, 
however, as far as I am aware, no organ can be pointed out as the 
undoubted seat of the sense in these animals. Generally speaking, 
the osphradium (Spengel’s olfactory organ) is said to be persistent 
in position and nerve-supply throughout the mollusca; but it does 
not appear to have been described in Helix and Limax.* In those 
molluscs, the sense has been variously thought to reside in the 
tentacles, the organ of Semper, and the pedal gland. Cuvier, from 
the nature of the skin, thought that a special organ might not be 
necessary ; and Simroth, more recently, has concluded that the 
it may reside, can hardly be doubted. Facts of the kind 
below have generally been regarded by authors as evidence of its 
existence; and it is perhaps worth mentioning, as showing 
I er 1 
in 1872, carbolic acid, diluted with water 
and sprinkled on the ground, will a¢¢ract and kill large numbers of 
1 Sir J. Lubbock, loc. cit., p. 140. 
* D. Sochaczewer, as quoted in J. R. Micr. Soc., (2), i, 24-55 
* Descent of Man, ed, 2, p. 18. 
+ E. R. Lankester, Art. * Mollusca,’ Encyc. Brit., ed. 9, xvi. (1883), 636, 660. 
5 Cuvier, quoted in Loudon’s ‘Mag. Nat. Hist.,’ iv. (1831), 530; Simroth, quo oted i 
‘ Zoological Record,’ 1876, Moll., p. 65 1881, Moll., p. 14; 1882, Maus is; 1883, ‘Moll, p26 
Naturalist, 
