270 THE GENESIS OF SPECIES. [CHAP. 



Now, as to tlie fact that sudden changes and sudden 

 developments have occurred, and as to the probability that 

 such changes are likely to occur, evidence was given in 

 Chapter IV. 



In Chapter V. we also saw that minerals become modi- 

 fied suddenly and considerably by the action of incident 

 forces as, e.g., in the production of hexagonal tabular 

 crystals of carbonate of copper by sulphuric acid, and 

 of long rectangular prisms by ammonia, &c. 



We have thus an antecedent probability that if changes 

 are produced in specific manifestation through incident 

 forces, these changes will be sensible and considerable, 

 not minute and infinitesimal. 



Consequently, it is probable that new species have 

 appeared from time to time with comparative suddenness, 

 and that they still continue so to arise if all the condi- 

 tions necessary for specific evolution now obtain. 1 



This probability will be increased if the observations of 



i Professor Humphry has remarked: "We are familiarized with the 

 fact that in the inorganic world combinations take place only in certain 

 definite proportions ; for instance, that oxygen unites with nitrogen in one 

 proportion to make nitrous oxide, in a second proportion, a multiple of 

 the first, to make nitric oxide, and so on to the fifth proportion or 

 multiple, which gives nitric acid, and that between these five several 

 fixed proportions no combinations take place : so that the resultants of 

 these and other similar combinations the inorganic species, as we may 

 call them are remarkably constant and fixed in their characters. Each 

 has its one form, as in the case of a crystal of chloride of sodium, or 

 sulphate of magnesk, which may be broken down or dissolved but which 

 cannot be modified or made to approach, still less to pass into, any other 

 form." "May there not be something analogous some corresponding 

 law of combining proportion presiding over living matter, educing the 

 various forms, fixing their characters, giving them constancy, in fact, 

 evolving and fixing the species?" Journal of Anatomy and Physiology, 

 vol. i. p. 11. 



