494 LESLIE E. AREY AND W. J. CROZIER 
of these differences, though certain of his statements could be 
better weighted with evidence. 
The general fact of the wandering of limpets from their scars 
has been known since the time of Aristotle, and the fact of hom- 
ing has more recently attracted the notice of a number of natural- 
ists (Bethe, '98; Davis and Fleure, '03; Pieron, '09a, '09b, 
'09c,'19; Bohn, '09; Orton, '14; Billiard, '14; Wells, '17). It is all 
the more curious that so little close experimental work has been 
devoted to the elucidation of the matter. Homing activities 
are shown by a number of more or less distinctly related forms — 
Patella, Siphonaria, Helicon, Fissurella, Calyptraea; among 
these, various degrees of 'homing' ability are manifest, and in 
Acmaea testudinalis, according to Willcox ('05 b), there is no 
evidence of this activity at all. 'Homing' is found to be success- 
fully executed by these animals even when they are artificially 
removed from their scar or from some point along their feeding 
path and replaced within a reasonable distance of the scar. For 
Patella, Pieron ('09 c) records successful returns following a 
displacement of 12 cm., while, in certain localities, the extent of 
the natural feeding journeys may be as great as 55 to 90 cm., 
according to various observers quoted by Pieron. For other 
genera less distances limit the mollusc's successful return to its 
home subsequent to experimental shifting — with Siphonaria, 
2 to 3 inches or perhaps a little more; for Fissurella, 2 inches 
(Willcox, '05 a). 
This kind of 'homing' has certain resemblances to that of 
Onchidium, yet there are noteworthy differences. Pieron notes 
that some individuals (Patella) wander little or not at all in 
securing food; these are easily 'lost,' and do not succeed in 
returning to their scars if even slightly displaced. Pieron 
regards the homing as dependent upon a permanent memory of 
the topography of the habitual situation, and upon a very 
exact memory of the relief of the spot on which the Patella 
orients itself according to the irregularities of its shell. i" He 
succeeded in demonstrating that a Patella could so orient itself, 
i»Cf. Pieron, '19. 
