1036 The Zoologist — January, 1868. 



Letters on Variation in Lepidoptera. By Edward Newman. 

 Letter the Third. — Pairs of Species. 



My dear Mr. Wollaston, — 



My third epistle treats of a matter which has already caused 

 much discussion, and will certainly cause much more before it is 

 finally accepted or rejected by our fellow-labourers in the field 

 of Science — I allude to the existence of pairs of species: and 

 here I wish expressly to state that I employ the word "species" 

 in its conventional and ordinary sense, and leave it a perfectly open 

 question for future discussion, whether the moieties of the pairs to 

 which 1 shall allude are species, races or varieties, or whether species 

 have any absolute existence in Nature. Such questions are here 

 avoided, because, however interesting and important as regards the 

 science of Natural History, they would rather encumber and confuso 

 the few simple views I am now endeavouring to express; but to my 

 point. 



It cannot escape the notice of the inquirer that natural groups of 

 organized beings exhibit a tendency to a dichotomous division : this 

 phenomenon is of frequent occurrence. Dr. Fleming, whose profound 

 teachings in Zoology have never been sufficiently esteemed, was the 

 first to point out the existence of this tendency ; his only mistake was 

 in assuming that a phenomenon which he saw so plainly portrayed on 

 Nature's face must involve the existence of an absolute law: he believed 

 that all Nature's laws were general ; he carefully studied the seen, and 

 imagined the unseen to be in exact accordance : now we may accept 

 the axiom of the poet that Nature 



11 Acts not by partial but by general laws," 



without assuming that we possess a perfect knowledge of those laws; 

 for instance, exceptions to natural laws may be of such frequent occur- 

 rence as to become laws themselves : it is an undoubted law that the 

 females of our own race produce but one young one at a birth, never- 

 theless an exception occurs quite as regularly, that once in a certain 

 number of births twins shall be produced : the exception by no means 

 vitiates the rule; indeed, in my estimation, it would tend to establish 

 the rule, but the exception must be regarded as having the same 

 force as the rule which it contravenes, and must never be disregarded 

 in our calculations or superseded by our inventions. 



