180 Miscellaneous. 



direction of the iuduced currents is reversed. The observation 

 may be repeated any number of times ; hut >io effect is prodticed 

 unless Ml interval of from ten to twenty seconds has elapsed since the 

 preceding irritation. 



h. If the part of the concave surface of the leaf which is nearest 

 the petiole is excited, whether electrically or mechanically, the 

 swing to the right (negative variation) is always preceded by a 

 momentary jerk of the needle to the left, i. e. in the direction 

 of the deflection due to the normal leaf -current ; if any other 

 part of the concave surface is irritated, this does not take place. 



i. Whether the leaf is excited mechanically or electrically, an 

 interval of from a quarter to a third of a second intervenes 

 between the act of irritation and the negative variation. 



MISCELLANEOUS. 



Observations on the E^vistence of certain Relations between the Mode 

 of Coloration of Birds and their Geographical Distribution, By 

 M. A. Milne-Edwards. 



In carrying on my researches on the geographical distribution of 

 animals in southern regions, I have been struck with certain relations 

 which seem to exist between the parts of the globe inhabited by birds 

 and the mode of coloration of those animals ; and wishing to know the 

 degree of importance that ought to be ascribed to this observation, 

 I have tried to examine more carefully than had previously been 

 done what may be called the geographical distribution of colours in 

 birds. In fact this investigation seemed to me capable of throwing 

 some light on the influence which local biological conditions may 

 exert upon the secondary zoological characters of species and races. 

 To furnish significant results it ought to bear principally upon the 

 natural groups which have a veiy wide geographical distribution ; 

 and in order that it m^y have the necessary degree of precision, it 

 ought to be founded upon the chromatic analysis of the plumage 

 and the comparison of its colours with well-defined normals. With- 

 out the aid furnished by the chromatic circles, for which science and 

 the arts are indebted to M. Chevreul, it would have been diflicult for 

 me to appreciate thoroughly the tones and shades which I had to 

 take into account, and still more difficult to formulate clearly the 

 results furnished by observation ; but by means of these circles this 

 labour has been remarkably facilitated. 



In a first series of investigations I attended specially to various 

 degrees of melanism ; and in order to judge of the relative influence 

 of black upon the plumage of birds inhabiting various geographical 

 regions, I took into account not only the extent of the parts of the 

 tegiamentary system which are tinted in that manner, but also the 

 degree in which the other colours may be dulled or modified in their 

 tone by mixture with black in various proportions. 



