546 NATURAL SCIENCE. snrr.. 



of some other class of adaptations. Mr. Romanes has little that is 

 new or original to say on this familiar subject, and we find the well- 

 known cases treated in the same familiar way. The resemblance 

 of the butterfly KaUima to a leaf is illustrated once more, here in an 

 uncoloured figure, which contrasts to great disadvantage with the 

 splendid chromo-lithograph in Mr. Beddard's book. As usual, no 

 information is given concerning the actual habits of KaUima in its 

 natural environment, the particular leaves which it resembles, or the 

 enemies which it deceives. The last sensational discovery by Mr. 

 Sclater, described by Mr. Poulton, of a homoptertius insect whose 

 body mimics a leaf-cutting ant, together with the leaf it carries, is 

 here reproduced ; but, as in the original description, no attempt is 

 made to show that the mimicry is of any advantage to the insect 

 which exhibits it. Another case given is the imitation of a venomous 

 snake by a non-venomous one, and considering the difficulty, even to a 

 naturalist, of distinguishing at first sight the innocence or otherwise 

 of any snake met with in its native home, it would have been by no 

 means superfluous if this case had been clearly proved to be one of 

 true mimicry. 



Chapter IX. is devoted to criticisms which have been put forth of 

 the theory of Natural Selection, and to some at any rate the most 

 interesting part of this chapter is that which deals with the electric 

 organ of skates and rays. Here the author, after giving an interesting 

 and detailed account of the structure and relations of these organs, and 

 discussing very impartially how its evolution can be explained on the 

 theory of Natural Selection, confesses with a candour which does 

 him the greatest credit that in the present state of our knowledge 

 such an explanation is quite impossible. He even goes so far as to say 

 that if a number of such cases could be produced, the theory of 

 Natural Selection would have to be discarded. 



The last chapter deals with the theory of Sexual Selection, which 

 the author warmly defends against Mr. \^'allace's criticisms. Mr. 

 Wallace's chief objection is that if the secondary sexual characters 

 supposed to be due to Sexual Selection are not necessarily correlated 

 with that fitness which nature selects, then the fit that do not possess 

 them would be selected, while if they are so correlated then it is nature 

 which really selects them and not the opposite sex. Mr. Romanes 

 states what in his judgment would have been Mr. Darwin's reply, 

 and in so doing presumably gives his own. It amounts essentially to 

 this : that secondary sexual characters are of too definite and 

 elaborate a kind to be regarded as the mere concomitant of that 

 exuberant health and vigour which are the result of Natural 

 Selection. It may be admitted, says the author, that a general 

 brilliancy of colour might accompany a general increase of vigour, but 

 it does not follow that the particular disposition of colours in the form 

 of ornamental patterns, and also elaborate special structures, can thus 

 be accounted for by Natural Selection. In this contention we 

 entirely agree. But Mr. Romanes is by no means successful in 

 avoiding the other horn of the dilemma. He merely says that "in 

 the phenomena of decorative colouring (as distinguished from merely 

 brilliant colouring), of melodious song (as distinguished from merely 

 tuneless cries), of enormous arborescent antlers (as distinguished from 

 merely offensive weapons), we have phenomena which cannot 

 possibly be explained by the theory of Natural Selection ; and, 

 further, that if they are to be explained at all, this can only be done, 

 so far as we can at present see, by Mr. Darwin's supplementary 

 theory of Sexual Selection." It seems to us that a much more 



