xi] CONCLUSION 147 



in number, so that the same assortment might not 

 infrequently be brought together even though the 

 group whose members exhibited the resemblance 

 might, owing to structural differences, be placed in 

 different families. 



We know from recent experimental work that 

 something of the sort is to be found in the coat colours 

 of different rodents. Agouti, black, chocolate, blue- 

 agouti, blue, and fawn form a series of colours common 

 to the rabbit, the mouse, and the guinea-pig. These 

 colours are related to each other in the same way in 

 these different beasts. In the rat, on the other hand, 

 there occur of this range of colours only the agouti and 

 the black. Each of these species again has certain 

 colour patterns which are peculiar to itself, such as 

 the "English" type in the rabbit, the tricolor pattern 

 in the guinea-pig, or the "hooded" variety in the rat. 

 The total range of colour and pattern is somewhat 

 different for each species, but a few are common to 

 them all. Moreover, there are others which are com- 

 mon to the mouse and the rabbit but are not found 

 in the guinea-pig, and others again which may occur 

 in the rabbit and the guinea-pig but have not been 

 met with in the other two. In certain features the 

 rabbit might be said to "mimic" the mouse, and in 

 other features the guinea-pig. It is not, of course, 

 suggested that the case of the butterflies is so simple 

 as that of the rodents, but so far as we can see at 

 present there would seem to be no reason why the 

 explanation should not be sought along the same lines. 



10—2 



