1899] A THORNY SUBJECT 5 



them in check. Features of less functional importance, as peripheral 

 characters, are the last to be controlled, and therefore present the 

 greatest diversity, while in this diversity spinosity is the limit of 

 progress." As to the causation of the two types of spines, Mr. 

 Beecher refers to the "general laws of organic change," — that is, the 

 stimulus or restraint of the environment, and the energy or deficiency 

 of growth force. Of these four causes two tend to produce spines like 

 those of Berbcris, two to produce the ornamental type as in Spondylus. 

 As no one of these causes is simple, and the action of each may 

 be assisted by secondary causes such as sexual selection, mimetic 

 influences, and so on, there are in all eleven causes of spine production, 

 all of which are discussed in detail with illustrative examples. 



The conclusions reached are, as indicated above, that on the one 

 hand spinosity represents the limit of morphological variation, and on 

 the other the decline or paracme of vitality. That is to say, alike in 

 ontogeny and in phylogeny spines increase until maturity, and there is 

 then in old age an " extravagant differentiation followed by a decline 

 of spinous growth, and ending in extreme senility with their total 

 absence." In other words, the great development of spinose organisms 

 in a group represents the beginning of the decadence of the group. 



Philosophy of Evolution. 



We cannot but welcome a paper of this type, more especially when, as 

 in Mr. Beecher's case, the evidence brought forward is largely palaeonto- 

 logical. No one who has toiled through pages of controversy as to the 

 probable action of natural selection in hypothetical cases, can fail to 

 appreciate a genuine attempt to discover what natural selection has 

 actually done in the past. But while recognising to the full the value 

 and excellence of Mr. Beecher's work, it is difficult to avoid criticism 

 of the frequent want of precision and clearness in his use of words, 

 especially in the treatment of the philosophical aspects of the subject. 

 The habit must, we think, lead sooner or later to much confusion of 

 thought. For example, is any good end attained by the introduction 

 of sentences like the following into a discussion of the question as to 

 whether variation is limited or unlimited : " As far as can be seen, the 

 limitations of the forms of species of animals and of plants end only 

 with the aggregate number of possibilities within the functional scope 

 of the organism. Beyond in either direction is death, and a passage 

 from the organic to the inorganic " ? The difficulty of comprehending 

 this statement is in no way diminished by finding that the author 

 seems to mean that variation is definite and orderly. Again, the author 

 states that certain types of spines have been produced by the "law of 

 repetition," which is " similar to induction in electrical physics, or to 

 the force or stimulus of example in human conduct." Is not this merely 

 biological mysticism ? We also hear much of the " forces of sexual 



