76 



^Vhi taker : Xotcs on Ba/s. 



The explanation of these spasmotlir and periodic instincts 

 towards gregarionsness may be arrived at by the collection of 

 a large number of exact observations ; even then it may liavc 

 to remain a mystery. 



One diliiculty in soh ing sucdi problems seems to me to l)e 

 so often overlooked, that 1 cannot refrain from mentionini:^ it. 

 Any characteristic, whether of structure or habit, in any 

 creature, acquired for a particular purpose by means of 

 natural selection, is not likely to be a benefit to the species 

 as a whole. Take, ■ for instance, au}^ example of protective 

 colouration : to whatever degree of perfection it may be 

 developed, such development would cease the instant that it 

 became perfectly protective. This implies that up to the very 

 last and most minute phase of the acquirement, the enemy 

 developes equally in cunning and perception. Reversion 

 always has a tendency to take place in a plastic organism, and 

 a moment's reflection only is necessary to show that no 

 creature can exhibit protective colouration, except to the exact 

 degi-ee which its enemies are capable of seeing through. The 

 degree in which it possesses protective colouration is the 

 measure of the enemies' keenness of observation, and can only 

 be in proportion thereto. The two things are two forces 

 acting upon one another, and must be in equilibrium. A 

 realisation of this fact is necessary to properly appreciate the 

 difficult}^ of solving many problems in natural history, because 

 it shows how a habit or characteristic may be acquired for 

 a specific purpose, and yet we may not be able to see that it is 

 fulfilling that purpose in any way. What we do see is only the 

 present position of two or more creatures, each striving to gain 

 an advantage over the other in the struggle for life. The 

 temporary advantage gained by either will not be beneficial 

 to the species as a species, but only to those individuals who 

 possess it more than the average of their contemporaries. 



On Plate III. are reproduced photographs of nine species of 

 bats found in this country, taken from some of my preserved 

 specimens, by Mr. Walter Wilson, for reproduction here. Nos. 

 I and 2 are from bats taken in Somersetshire ; all the others 

 are from Yorkshire specimens. 



The Greater Horseshoe Bat shown in different positions on 

 Plate II., was one of my pets which I lent for a time to Mr. 

 Riley Fortune, who kindly took these photographs of it. Figs. 

 I and 2 are ventral and dorsal views of the bat, sleeping. 



Naturalist, 



