2 24 



NATURE 



[July i8, 1872 



" Natural Selection." The conditions under which they 

 live are so completely similar, that it docs not appear what 

 ground there can be for difference in the characters best 

 htting the possessors for survival in the diflercnt valleys 

 in which they arc found. The vegetation is much the 

 same ; the bird and insect enemies, so far as they have 

 any, are the same. The north-east side of the mountain 

 range is a little more rainy than the opposite side, but this 

 does not account for the dilTerent forms found in the suc- 

 cessive valleys on the same side of the range. In what 

 respect can the conditions of survival lov:\\\ch Achntiiwl/ii 

 Sku'aiii\% subjected in Manoa, differ from those under 

 which A. producia lives in Makiki, only a mile distant, or 

 from those in which A. varia is placed in Palolo, three 

 miles away? There is no reason to doubt that some 

 varieties less htted to survive have disappeared ; but it 

 does not follow that the "Survival of the Fittest" — (those 

 best fitted when compared with those dying prematurtly, 

 but ec|ually fitted when compared with each other)— is tlie 

 determining cause which has led to these three species 

 being separated from each other in adjoining valleys. The 

 " Survival of the Fittest " still leaves a problem concern- 

 ing the distribution of those equally fitted. It cannot be 

 shown that the "Survival of the Fittest" is at variance 

 with the survival, under one set of external circumstances, 

 of varieties differing more and more widely from each 

 other in each successive generation. The case of the 

 three species under consideration does not seem to be one 

 in which difference of " Environment" has been the occa- 

 sion of different forms preserved in the different localities. 

 It is rather one in which varieties resulting from some 

 other cause, though equally fitted to survive in each of the 

 three localities, have been distributed according to their 

 affinities in separate localities. There is no reason to 

 think that A. producta is not as well fitted to live on the 

 Kukui trees that abound in Manoa and Pololo, as on the 

 same trees in Makiki. Again, is the " Survival of the 

 Fittest " sufficient to explain their being kept within these 

 extremely narrow limits since they were produced ? One 

 would at first suppose that, in the course of a few years, 

 or in a few hundred years at the farthest, the three species 

 .would have been diffused throughout this area of only five 

 or six square miles which is now divided between them. 



We seek in vain for an explanation of these facts in the 

 still further principle of variation, set forth by Herbert 

 Spencer under the effects of change in use, and discussed 

 by Prof Cope under the names of " Acceleration and Re- 

 tardation." This cause of accelerated variation has in- 

 fluence only where there is a difference in the "use, either 

 compulsory or optional." If, on the one hand, the 

 change is compulsory, it must be owing to a change in 

 external circumstances. But in the case of these three 

 species we are unable to find any difference in their circum- 

 stances requiring change. Their enemies are the same, 

 the climate is the same, and they undoubtedly eat the 

 same food, for the chief resort of all is the Kukui tree. 

 If, on the other hand, the change in the use is optional, 

 and without reference to change in circumstances, it be- 

 longs to the class of spontaneous variations, and does not 

 explain why those of one type of variation (or of one kind 

 of choice) should be brought together and limited to so 

 small an area. 



Ri-latio)is of tlic Genera 



The relations of the genera of Achatinellinrc involve 

 problems of still greater interest, but more difficult to 

 penetrate. The limits of this paper render it impossible 

 to do more than to give some of the most striking facts, 

 and indicate some of the questions that arise. 



Through the varieties oi A.oviforDiis andi). Sowerbyana, 

 the genus .■\ihatinclla passes by minute gradations into 

 BuUinclla ; but connections of this kind have not been 

 noted between the other genera. 



The family is divided into two natural groups of genera. 



The first group consists of seven genera : AchalineUa, 

 Bulhnclla,Hcliitcii'Ua.Paitiil!na, IScciicoiiilna^Lavtiiiclla, 

 and Aiiriculclla. These are all arboreal in their habits. 

 In form they are either sinistral, or both dextral and 

 sinistral. The second group consists of three genera : 

 A nins/m, LcpldcJiatiiia, and Carelia. With but few excep- 

 tions, the species of Ainasfra and Lcptailiati)ia live on 

 ihe ground and are of dextral form. I am not informed 

 concerning the habits of Caiclia, but the structure of 

 the shell and its invariably dextral form show that it 

 belongs to this group. 



Of the second group, Carclia is found on Kauai, the 

 most western of the Sandwich Islands. The two remain- 

 ing genera are found on all the islands. The first, or 

 arboreal group, is represented on all the islands except 

 Kauai. The separate genera are more restricted in their 

 distribution. Two are found only on Oahu, a third on 

 Oahu and Molokai, a fourth on Molokai and Maui, and 

 the remaining two on several islands. 



The genus Helix is represented on all the islands. So 

 far as I know, the species all live on the ground, and are 

 all dextral in form. They are all small in size, with spire 

 very much depressed, and have no trace of the peculiar 

 twist in the columella which characterises the Achati- 

 nellina;. 



Why should nearly all the ground species be dextral, 

 and many, if not a majority, of the arboreal species be 

 sinistral ? Does this fact point to one common 

 origin for the arboreal genera, and a separate origin 

 for the ground genera ? Or are we to suppose that ar- 

 boreal habits tend to produce sinistral forms ? The few 

 species of Ainastia which are found on trees retain the 

 de.xtral form that belongs to the allied species living on 

 the ground. 



Facilities needed for the Study of Variation of Species 



I am fully persuaded that the study of allied forms 

 in their geographical relations is one of the richest fields 

 open to the naturalist. He may here reap a harvest of 

 facts throwing light on many of the questions that are 

 now occupying the special attention of the scientific 

 world. 



To afford suitable opportunity for such studies, it is 

 necessary that certain sections of our museums should 

 be devoted to the exhibition of objects in an arrangement 

 more strictly geographical than anything that has yet 

 been attempted. The leading feature in the arrangement 

 adopted by Agassiz in the museum at Cambridge, Massa- 

 chusetts, is the geographical grouping of objects ; but for 

 the fuller presentation of the curious facts of geographi- 

 cal distribution, it is further needed that in certain wisely 

 chosen families the objects should be laid down in their 

 actual geographical relations, as on a map. It is not 

 necessary that the map on which they are arranged should 

 be as mathematically correct as a nautical chart. It will 

 be sufficient if cases are prepared, approximately repre- 

 senting the territory or territories chosen, with subdivisions 

 representing the different localities in which the specimens 

 have been found. 



Collections for such a purpose should be made with 

 scrupulous care. The locality of every object should be 

 noted with great minuteness. In collecting shells at the 

 Sandwich Islands, noting the name of the island is not 

 sufficient, nor yet the name of the district. Each valley, 

 with its area two or three miles in length, and but one or 

 two miles in width, needs to be separately explored, and 

 all the shells labelled with the name of the valley. To 

 show the relations of the species to each other, as com- 

 plete a series as possible should be obtained of the count- 

 less varieties. 



For this kind of study the fauna of the Sandwich Islands 

 is of peculiar interest, on account of the number of forms, 

 and the variety of relations presented within a small com- 

 pass, John T. Guj.ick 



