462 Chronicles of Science. [July, 



getlier differing from herself." Local forms or varieties are, it appears 

 to us, scarcely distinguishable from races or subspecies, except that 

 the differences are slighter, but surely this is not sufficient to consti- 

 tute a distinct phenomenon. The coexisting variety " is a somewhat 

 doubtful case." It is " when a permanent and hereditary form exists 

 in company with the parent or typical form, without presenting those 

 intermediate gradations which would constitute it a case of simple 

 variability." This can only be distinguished from dimorphism by 

 direct evidence of the two forms breeding separately. Maces or sub- 

 species : " these are local forms completely fixed and isolated," and, as 

 we have already said, are treated by Mr. Wallace as species. As, 

 however, it is admitted that " these may and probably have been de- 

 rived from a common stock," it seems more convenient to use the word 

 subspecies than to obliterate the distinction between an ordinary well- 

 marked form and what is avowedly often only a slight though perma- 

 nent modification, by calling both species, albeit it may be desirable 

 in some cases that they should have a specific name. 



Species. — Here Mr. Wallace, notwithstanding the Pritchard defi- 

 nition, confesses that " we have no means whatever of distinguishing 

 so-called ' true species ' from local forms and varieties ; but the expe- 

 rience of any one who has studied any large family of insects will 

 confirm this assertion that in many instances ' not single species but 

 whole groups ' have, from the accumulation of materials, been proved 

 to have ' no definite specific limits.' " 



This is, however, scarcely sufficient to prove the origin of species by 

 variation and selection, though it shows that the permanence of species 

 is not to be depended on within any limits than can at present be 

 defined. 



So far as the phenomena of variation among the Papilionidfe are 

 influenced by locality, Mr. Wallace has come to the following conclu- 

 sions : — 1, the species of the Indian Region (Sumatra, Java, and 

 Borneo) are almost invariably smaller than the allied species inhabit- 

 ing Celebes and the Moluccas; 2, the species of New Guinea and 

 Australia are also, although in a less degree, smaller than the nearest 

 species or varieties of the Moluccas ; 3, in the Moluccas themselves 

 the species of Amboyna are the largest; 4, the species of Celebes 

 equal or even surpass in size those of Amboyna ; 5, the species and 

 varieties of Celebes possess a striking character in the form of the an- 

 terior wings, different from that of the allied species and varieties of all 

 the surrounding islands ; 6, tailed species in India or the Indian Eegion 

 become tailless as they spread eastward through the archipelago. 



We are unable to enter into any of the numerous details given 

 in illustration, but they furnish in the author's opinion " a strong 

 corroborative testimony in favour of the doctrine of the origin of 

 species by successive small variations." As to the causes which have 

 led one group of butterflies to imitate another, the author agrees with 

 Mr. Bates, that the object of mimicry " possesses some means of defence 

 (probably in a peculiar odour or taste), which saves it from attack," 

 and the imitating groups " thus gain an advantage in a freedom from 

 persecution similar to that enjoyed by those they resemble." It would 



