ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 559 



species, e.g., of butterflies, have survived in virtue of the mimetic habit, 

 it is difficult to understand why other non-mimetic and non-immune 

 species should be equally or more numerous under the same external 

 conditions. Obervation shows, too, that many species which resemble 

 non-living objects often lose any possible advantage from the resemblance 

 by moving at the critical moment. 



That the phenomena of mimicry should have originated through 

 natural selection the author regards as not only improbable, but incon- 

 ceivable without the aid of the metaphysical conception of purposeful 

 endeavour. He believes that recent investigation has already established 

 that colours, markings, and forms arise in accordance with definite laws 

 working of necessity, without exception, and with no reference to utility. 

 The markings on the wings of grasshoppers, praying mantises and the 

 like, are due to innate constitutional causes, and their resemblance to 

 sticks, leaves, etc., seem to him simply a phenomenon of convergence. 

 Further study and more definite experiment are required, but, if these 

 are to lead to a deeper understanding of the evolution of colour and 

 markings, they must be untrammelled by the preconceptions of the 

 popular theory of mimicry. 



Reactions of Amphibians to Light.* — A. S. Pearse has made an 

 experimental study of the reactions of Amphibians to light, with the 

 view of ascertaining more fully the photoreceptors involved, and deter- 

 mining the part played by the central nervous system in these reactions. 

 The following Amphibians were found to be positively phototropic : 

 Biemyctylus virklescens, Rana clamata, R. palustris, Bufo fowleri, B. 

 americanus ; and the negatively phototropic species studied were : 

 Necturus maculosus, Cryptobranchus allegheniensis, AmbJy stoma puncta- 

 twn, Plethodon cinereus. Most of these species, after removal of their 

 eyes, gave photic responses which were like those of normal individuals. 

 The photic reactions of eyeless Amphibians are not due to the direct 

 stimulation of the central nervous system or the exposed ends of the 

 optic nerves by light, but to the action of the skin as a photoreceptor. 

 Mechanical stimulation (handling) does not change the character of the 

 photic reactions, though it makes them more evident by inducing loco- 

 motion. 



Toads which are stimulated by light through the eyes alone, react 

 in the same manner as individuals stimulated through the skin, or 

 through both the skin and the eyes. The movements of eyeless toads, 

 stimulated unilaterally by light from above, are toward the illuminated 

 side ; and toads stimulated through one eye only from in front do not 

 go toward the light, but turn towards the illuminated side. The photic 

 reactions are therefore due to differences in light intensity on the two 

 sides of the body, and the direction of the rays is ineffective. After 

 the eyes had been removed, Cryptobranchus and Necturus were most 

 responsive when the tail was illuminated, but the skin of the toad is 

 apparently of equal sensitiveness in all parts of the body. A prolonged 

 period passed in light or darkness had no effect on the phototropic 

 responses of the toad. Cryptobranchus is strongly photokinetic, but in 

 the other Amphibians tested, this quality was not strongly developed. 



* Proc. Airier. Acad., xlv. (1910) pp. 161-208 (7 figs.). 



