December 27, 1900] 



NA TURE 



201 



of " explaining " things by Lamarckism or any other 

 hypothesis ; but as this method is freely indulged in 

 throughout the book, and since Mr. Cunningham is 

 nothing if not logical, it may be well to examine a little 

 more critically his position in this respect. The kind of 

 assumption to which reference is made is well illustrated, 

 not only by the chapter on insects, where colour is chiefly 

 dealt with, but also in other classes where structures of 

 unknown use are possessed by the males. Thus, among 

 birds, the males of Chasmorhynchus nudicollis and other 

 species of the genus are supposed, without evidence from 

 observation, to fight and to 



"seize their adversaries by the skin at the base of the 

 beak, the attack being directed to the chin or the fore- 

 head, according to the species" (p. 145). 



This is put forward as a " probable conjecture," because 

 the male characters require such Lamarckian stimula- 

 tions to account for their presence. Among chamreleons, 

 the male, C. Owenii, has three slender horns which are 

 not known to be used for fighting ; 



" but the animals are known to be quarrelsome, and it is 

 probable that the appendages are thus used " (p. 166). 



In this case the author even allows his logic to go by 

 the board, because he follows up this statement, which is 

 only conjectural, with the remark : 



" Here again, therefore, we find that the existence of out- 

 growths corresponds to the impacts produced by definite 

 actions, both being confined to the male sex." 



That is to say, that a function which is conjectured to be 

 probable in one sentence is treated of as an established 

 truth in the following sentence. Examples of this kind 

 might be multiplied, but the foregoing will suffice. Now 

 the point which the writer of this notice wishes to urge 

 is that all the arguments of this class are arguments of 

 analogy only, and the weight which attaches to them is 

 dependent on the antecedent probability of the hypo- 

 thesis in support of which they are brought forward. 

 Mr. Cunningham has, by implication, admitted the 

 antecedent probability of Lamarckian factors ; but if 

 we do not follow him— and no selectionist will— much, 

 if not all, the force of the analogies is lost, and 

 "we have a right to demand proof of actual con- 

 nection between male structures and their use in 

 every case described by the author. It is not to the 

 point, in such cases, to urge that because in one 

 species the male has been seen to use appendages or 

 excrescences for fighting, therefore in other species with 

 similar growths these must be used for the same purpose. 

 The theory of sexual selection allows that male characters 

 of the kind referred to may have been developed for 

 ornament or as weapons of attack or defence, or for 

 both purposes. But Lamarckism must have a definite 

 mechanical cause for each excrescence or appendage, 

 and the failure to discover such cause in any particular 

 case is so fatal to the doctrine that most impartial 

 readers of Mr. Cunningham's work will, on this ground 

 alone, reject his conclusions. In one case {Turntx 

 taigGor^ p. 118) where the females are known to fight, 

 and where there is no modification of structure corre- 

 sponding to this habit, the author suggests 

 NO. 1626, VOL. 63] 



" that the pugnacity of the females has but recently arisen 

 in the evolution of the genus, but it may be that the 

 wounds inflicted are not very severe" (p. 120). 



Many other points in the volume under consideration 

 are open to criticism, and, in view of the importance of 

 the issues, demand notice. Reverting again to the 

 chapter on mimicry, the author, in rejecting the obviously 

 simple explanation offered by selection for protective 

 purposes, says that 



" the theory of specific mimicry involves assumptions 

 that have not been sufficiently realised. It assumes that 

 birds or other enemies of butterflies are as precise in 

 entomological discrimination as the human specialist" 

 (p. 241). 



This is hardly a correct statement of the case ; the 

 assumptions made by the theories of mimicry (Batesian 

 and Miillerian) have been thoroughly well realised, and 

 a body of evidence, both observational and experimental, 

 has been brought to bear upon these theories, which 

 Mr. Cunningham has either overlooked or chooses to 

 ignore. But his own assumption, which precedes this 

 statement, displays such an astonishing misapprehension 

 of the whole subject that we can only come to the con- 

 clusion that the author has not really made himself 

 master of the theory which he is endeavouring to over- 

 throw. Having admitted that mimicking forms may 

 belong to persecuted groups, he still suggests that, after 

 all, the mimics may not owe their safety entirely to 

 deceptive appearance^ and he then goes on to say :— 



" Inedible forms, such as the Heliconidas, the goose- 

 berry caterpillar and others, are distasteful largely in con- 

 sequence of the presence of the pigments which make 

 them conspicuous. Therefore when a mimicking form 

 acquires similar pigments it probably likewise ceases to 

 be palatable to insect eaters, and would be equally un- 

 molested even if it possessed no particular resemblance 

 to a species of another family " (p. 241. Italics ours.) 



It really appears from this as though the author 

 believed that the mimicry extended to similarity of pig- 

 ment, which is not only contrary to the truth, as established 

 by the researches of Mr. Gowland Hopkins, but is in 

 Itself so improbable a priori that it is surprising that Mr. 

 Cunningham should have committed himself to the 

 statement. 



Considered as a whole, there can be no doubt that this 

 fifth chapter is the least satisfactory in the book. It not 

 only contains misstatements such as the above, but its 

 omissions show that the author has not made himself 

 acquainted with the recent developments in this direc- 

 tion. As the Arachnida are not considered at all, the 

 splendid observations of Mr. and Mrs. Peckham on the 

 courtship of spiders are not discussed. The reference 

 to Poulton's experiments on the influence of the colour of 

 the surroundings on the colour of the larva and pupa, as 

 an illustration of the modifying action of the " quality of 

 the light" (p. 231) upon the colour of the wing of a 

 butterfly, is a false analogy. The statement (p. 248) that 

 " the beauty of a butterfly's wing is equally visible when- 

 ever the insect flies " does not convey the whole truth, 

 because in many of the most gaudily coloured males the 

 full splendour of the colour is only seen from the front 

 aspect, i.e. facing the insect ;and looking across the 



