INTRODUCTORY. 13 



Occasionally, a fortunate concurrence of circumstances must 

 have removed the difficulties in the case of wild animals. 



It is recorded in the " Proceedings " of the Zoological 

 Society for 1860 (p. 206), that nine albino moles were captured 

 iii a field near Beckenham, in Kent. These may have been, it 

 is suggested, the offspring of one pair ; but more probably this 

 was not the case, since moles usually produce only four or five 

 young ones. Here, be it observed, the white moles were in a 

 position to find a mate, and therefore the colour was handed on 

 to their progeny. 



In the Zoologist * Mr. Stevenson recorded that a pair of 

 albino night-jars were shot in the year 1850. The night- 

 jar is a very invariable bird, and so the fact is of interest, if 

 only as a record of variation. Moreover, white is a particularly 

 unfavourable variation in a crepuscular bird, coloured, as the 

 night-jar is, with hues entirely suitable to the dusky sur- 

 roundings of late evening. The isolated occurrence of even a 

 pair is not by itself, perhaps, a very remarkable fact as bearing 

 upon the question at hand ; what is more remarkable and 

 important is the fact that an adult bird, also albino, was shot 

 near the same place in 1858,t and another in 1859 ; this 

 suggests a case of heredity of a variation most unfavourable to 

 the well-being of the species. 



In the same .Journal i the existence of sixteen or eighteen 

 yellow rabbits in several adjacent warrens is recorded. This is 

 clearly a very large number of individuals of an unfavourable 

 variation. They disappeared, however, after the winter. 



It would be of great importance to collect statistics of 

 variation occurring in nature ; but it is unnecessary to point 

 out the great difficulties that would attend this line of investi- 

 gation. 



* xiv./ip. 5278. f P- 6779. \ p. 



