594 



SCIENCE. 



[N. S. Vol. XXII. No. 567. 



element in the evolution of specific types. 

 His papers have been useful in putting a 

 needed emphasis on a factor which had been 

 insufficiently taken into account and fre- 

 quently overlooked by theorists concerned 

 with the question of specific evolution. It 

 was appropriate, therefore, that the Carnegie 

 Institution should give him the opportunity 

 of presenting in one handsome volume, the 

 ripened result of his years of reflection and 

 study on this subject. 



It is known that his studies were largely 

 due to the interest excited by the beautiful 

 and multiform tree-snails of the Hawaiian 

 Islands, which, for variety in characteristics 

 elsewhere usually taken as of specific value, 

 are unexcelled in any equal area. It was a 

 problem which appealed to every collector of 

 these attractive animals. How should this 

 almost infinite variety under almost identical 

 conditions be accounted for? The latest in- 

 vestigations indicate that the chief food of 

 the arboreal Achatinellas consists of fungoid 

 mycelium which in the warm air and con- 

 stant rains of the mountainovis region of the 

 islands is more or less abundantly developed 

 on the bark of trees and shrubs upon which 

 these landshells live; an examination by Mr. 

 Cook of many stomachs has shown that the 

 leaves of the shrubs or trees form no part of 

 their diet, and that, contrary to the opinions 

 formerly held and even not altogether dis- 

 carded in the volume under review, the species 

 of tree upon which these animals live is not 

 of importance in their economy; the same 

 species of shell being often found indiSer- 

 ently upon different species of trees over the 

 area the former inhabits. This fact lends 

 even greater importance to the remaining ele- 

 ments of the environment among which the 

 stimulus to variation is to be sought. 



It has been found that the Achatinellas do 

 not lend themselves readily to experiment. 

 Hemoval, even when not the slightest injury 

 has been inflicted, usually proves fatal, from 

 some unexplained cause. It is evident that 

 they are extremely sensitive to even minute 

 changes in altitude, moisture, etc., and at- 

 tempts to get them to breed in the more ac- 

 cessible regions of the islands, where they 



could be kept under continuous observation, 

 have so far proved failures. Even the eggs 

 seem unable to bear transportation. 



Tor the reader who wishes to gain quickly 

 an idea of the hypothesis maintained by Dr. 

 Gulick, we should suggest the original papers 

 of which a bibliography is given in the pres- 

 sent volume, as they contain the meat of the 

 matter in more concentrated form. In the 

 opinion of the reviewer something has been 

 lost by the considerable expansion of verbiage 

 to which the statement of the hypothesis has 

 here' been subjected. But doubtless the special 

 student of these recondite problems will find 

 the volume none too long. In any event it 

 should not be forgotten that while Dr. Gulick's 

 views seem eminently probable and in the re- 

 viewer's mind go far toward accounting for 

 many of the facts, nevertheless they are 

 theoretical and have not yet been subjected 

 to the crucial test of experiment, by which the 

 proposed theory in the end must be tested. 

 To justify final acceptation an hypothesis 

 must not only be capable of accounting for 

 the facts but it must be shown to be the only 

 one by which they may be adequately ex- 

 plained. It is also necessary to determine 

 how far the animals in question have arrived 

 at that state of organic equilibrium which we 

 recognize by the name of species. If, as has 

 been held by some authorities, the small color- 

 groups are really only of a temporary nature, 

 and liable to immediate change upon subjec- 

 tion to modified environment, then the au- 

 thor's hypothesis, while losing nothing of its 

 truth, is not a eontribution to the evolution 

 of species so much as to the physiology of 

 color-variation. The latter may or may not 

 be, in the group discussed, a factor of specific 

 weight. 



In any case we are grateful for the full pres- 

 entation of the author's views which are of 

 acknowledged importance in the discussion. 

 The volume is well printed, though we could 

 have wished that the colored plates had been 

 of a better quality. W. H. Dall. 



Marceli NencJci Opera Omnia. Gesammelte 

 Arbeiten von Professor M. Nencki. Braun- 

 schweig, Friedrich Yieweg und Sohn. 1905. 



