CONTENTS xiii 



4. The tendency to the accentuation or undue prolongation of 

 Particular Stages ; best seen in cases of abrupt transformation or 

 metamorphosis. 



5. The tendency to the acquisition of new characters, through the 

 action of Natural Selection. 



Tests of Recapitulation. All stages must be possible ones, and each 

 stage must be an improvement on the preceding one. The eyes 

 of Cuttle-fish. 



Embryonic Stages regarded as Ancestral Forms. The egg is the 

 equivalent of the Protozoon stage. 



LECTURE V. (Pp. 116-150.) 

 THE COLOURS OF ANIMALS AND OF PLANTS. 



Colour may be non-significant, as in the case of the redness of the 

 blood of many animals, or the colours of animals living in dark- 

 ness. More usually, however, colour can be shown to have a 

 direct relation to the welfare of the individual or species, and to 

 be attributable to the action of Natural Selection. 



Of late years our knowledge on this subject has advanced 

 greatly, mainly through the observations of Mr. Wallace, sup- 

 plemented by those of Mr. Bates, Mr. Trimen, Mr. Poulton, 

 and others. 



COLOURS OF ANIMALS. 

 1. Apatetic Coloration. 



Apatetic Coloration serves to hinder recognition : it may be 

 considered under three heads : — 



(a) Protective resemblances : aiding escape from enemies. The 

 resemblances are usually either to plants, as in the case of the 

 leaf insects, and stick insects, and of the green coloured cater- 

 pillars and other frequenters of plants or trees ; or else to 

 inanimate objects, as in the case of the whiteness of the Arctic 

 Hare, and of other defenceless Arctic animals. 



A peculiar and interesting form of protective resemblance is 

 afforded by the cases of mimicry, in which a defenceless butter- 

 fly or other animal escapes attack through its superficial 

 resemblance to a noxious or venomous animal. 



(b) Aggressive resemblances are cases in which the object 

 gained, like that of the wolf in sheep's clothing, is to facilitate 

 approach to the prey through a superficial resemblance to other 



