THE SPECIES CONCEPTION. XXXI 



but the comparison is vitiated by the uncertainty whether the 

 same colonies were found. The older collections were not 

 closely enough localized to afford evidence of progressive 

 change. In many cases it is certain that they were from 

 districts now deforested. The accurate record of colonies now 

 kept by the best collectors will permit of such comparisons in 

 the years to come, and if the snails are not exterminated, in- 

 valuable evidence for evolution will be available for Hawaiian 

 students of fifty years hence, or even less. Answers may be 

 found to such questions as the appearance of mutations, their 

 influence on the colony and their fate, and the permanency or 

 changes of hybrid and pure colonies under natural conditions, 

 etcetera. In this connection, suggestive observations were 

 made by Mr. Thaanum on a colony of Partulina proximo,, re- 

 visited after an interval of twelve years. In the interval, an 

 apparently new mutation shells with pale greenish ground 

 had dispossessed the normal white-ground shells which alone 

 were found twelve years before (see p. 360). 



While there are good reasons for the belief that color 

 mutations of considerable amplitude are common in Acha- 

 tinella, it must be remembered that there is no actual evidence 

 bearing on the production of species of the first grade, in other 

 words, real species, by mutation. 



Observations on the snails of many regions has led me to 

 believe that the well-defined species are often, perhaps usually, 

 rather complex populations of individuals differing in many 

 minor but heritable characters, such as size, minutiae of shape 

 and sculpture, number of teeth on the radula etcetera. In 

 Achatinella, as in Liguus, Polymita, Amphidromus etc., the 

 versatile character is the very conspicuous one of color, and 

 therefore has attracted far more notice than equally im- 

 portant but less noticeable characters in plainer snails. 



One condition favoring intense speciation in the Hawaiian 

 Islands is that the snails breed and grow all the year round. 

 Hence, in a given time, their evolution should be at least 

 twice as fast as that of snails in temperate latitudes, in which 

 the organism is quiescent more than half of the time. This of 

 course applies to humid regions in the tropics in general. 



