310 ANNUAL OF SCIENTIFIC DISCOVERY. 



disease, anrl the tendency to revert to tlie original type. So that 

 increasinj^ departure requires greatl}' inereasins: care ; and we do 

 not know that any amount of care and time would be sufficient to 

 produce what nii2,'ht fairly be called a new species. The bring- 

 ing about any marked change, by Nature's selection, is shown to 

 be very hard of proof, and has ojjposed to its probal)ility the fact 

 that the members of a species which are most unlike have the 

 greatest tendency to i)air, and are the most fertile ; so that we 

 have here, in addition to the ready ri'version of niodilied breeds to 

 the original stock, a law by which the growth or perpetuation of 

 peculiarities is prevented, and a constancy given to the characters 

 of the species. This law is more striking from its contrast with 

 the bar that exists to the i)airing of different species, and the 

 infertility of hybrids. Within a given i-ange, dissimilarity pro- 

 motes fertility. IJcyond that range, it is incompatible with it. 



These, and otlu'r considerations, have always inclined him to 

 the opinion tiiat modifications of animal type, occurring in nature, 

 are more likely to be the result of external influences operating 

 upon successive generations, influencing their development, their 

 growth, and their maturity, than of "natural selection" and the 

 " struggle for existence." 



The slight variability of animal types through long periods, the 

 clear manner in which many of them are worked out from one 

 another, and which increasing investigation seems to render more 

 and more apparent, make the prospect of jiroving that they are 

 educed from one another by any of the hitherto supposed processes 

 gi'ow more and more distant, and the feeling arises that there must 

 be some other law at work which has (escaped our detection. 



Whatever be the law and forces which effect and regulate the 

 evolution of species, they are prol)ably of the same kind as those 

 which are operating in the inorganic world. The orderly and 

 definite manner in which forms and features and si)ecific charac- 

 ters are given and jireserved in one instance, may be assumed to 

 be of the same nature as in the other ; and we must i>i'obably 

 refer the fixed animal and vegetable types to influences identical 

 with, or similar to, those by which the forms are assigned to crys- 

 tals, and the stratification is given to rocks, by which the geologi- 

 cal epochs have been determined, and the boundai"ies of our plan- 

 etary and solar systems have been set. One cannot but think that 

 it may be within the power of man to work out and to comjire- 

 hend, in some degree at least, the principles l)y which these breaks 

 in the organic and inorganic worlds, constituting as they clearly do 

 an important feature in the plan of creation, are brought about and 

 regulated. 



In connection with this subject may be mentioned a paper pre- 

 sented to the same Association by Mr. A. R. Wallace, 



On Beversed Sexual Characters in a BuUerJty, and their Interpre- 

 tation on the Tlieory of Modifications and Adaptive Mimicry. — In 

 this pajjcr, the author, who is an independent originator of the 

 theory advanced by Darwin, gave the result of some of his own 

 and Mr. Bates's observations on the origin of species in Lepidop- 

 tera. The Heliconidas, a group of butterflies with a powerful 



