148 



NATURE 



'October 25, 191 7 



THE STUDY OF A GENUS OF LAND 

 SNAILS.-^ 



THE Rev. J. F. Gulick, in an important 

 paper published by the Linnean Society in 

 1873, described the distribution of the land snails 

 belonging to the family Achatinellinae that are 

 found in the Hawaiian islands, and pointed out 

 that neighbouring valleys in these islands, 

 although presenting the same environmental con- 

 ditions, are inhabited by distinct species. He 

 regarded this as an example of a diversity of 

 evolution under one set of external conditions 

 which was rendered possible by isolation in the 

 different valleys. 



Darwin had stated in "The Origin of Species" 

 that isolation is an important element in the modi- 

 fication of species through natural selection. But 

 if the environmental conditions in the localities 

 inhabited by distinct species are in all essential 

 respects the same, natural selection takes no part 

 in the evolution of species, and we must assume 

 some inherent tendency to evolution, some vis a 

 tergo which works along definite lines of diver- 

 gence independently of external conditions. The 

 question is one of very great importance, and 

 further investigations both on the variations of 

 the shells and on the conditions of their environ- 

 ment were greatly needed. In the magnificent 

 memoir before us Prof. Crampton supplies the 

 materials for reopening the discussion. 



Partula, belonging to the family Bulimulidag, 

 is one of the genera of snails, confined to certain 

 islands in the South Pacific Ocean, which show 

 a distribution of distinct species in adjacent 

 valleys similar to that of the Achatinellinae in 

 Hawaii. 



The author has collected and examined an enor- 

 mous number of shells, has personally studied the 

 habits of the snails in their localities, and has 

 put together his copious notes on the vegetation, 

 meteorology, and topography of the islands. The 

 present volume deals only with the species of 

 Tahiti, but we are promised further volumes on 

 the species of the genus from other localities. 



As a detailed study of a single genus, however, 

 this volume is the most complete of anything of 

 the kind that has yet been attempted, and we 

 may congratulate the author on the conclusion 

 of this the first stage of his most laborious task. 



To illustrate his study of the local conditions, 

 we are provided with a large number of maps and 

 sketches of a topographical model of the island, 

 . with many excellent photographs of the vegeta- 

 tion, and with tables of temperature and rain- 

 fall ; and to illustrate the species he describes 

 there are fifteen excellent coloured plates. For 

 each of the species and varieties of the species in 

 the islaqd the author gives us the mean value 

 of the measurements of the shells and of the 

 apertures of the shells, together with the stan- 

 dard deviation, and in many cases the results are 

 plotted out in frequency polygons. 



1 " Studies on the Variation. Distribution, and Evolution of the Genus 

 Partula." By Prof. H. E. Crampton. Pp. 342 + 34 plates. (Carnegie 

 In.stitution of Washington, 1916.) Price 15 dollans. 



NO. 2504, VOL. 100] 



Limitations of space do not permit further 

 reference to the details given in this very laborious i 

 piece of work — ^a work which will prove essential 

 to those who are interested in the problem of the 

 differentiation of species. 



It may be disappointing that the author does 

 not state more decisively what his conclusions 

 are from this elaborate study, but, although the 

 material is already so extensive, it is perhaps 

 wise, on his part, to delay his statement of con- 

 clusions until the series of memoirs is completed. 

 It is clear, however, that the author is convinced 

 that differences of environmental conditions can- 

 not be held responsible for the differentiation of 

 the species and varieties. In dealing with the 

 widely spread species, Partula otaheitana, for 

 example, he says that "the role of the environ- 

 ment is to set the limits to the habitable areas, or 

 to bring about the elimination of individuals 

 whose qualities are otherwise determined — that 

 is, by congenital factors " ; but, of course, there 

 is no suggestion as to the cause of the change or 

 diversity of the congenital factors. 



The facts that are given in various chapters 

 which seem to have a bearing on Mendelian in- 

 heritance are, as the author admits, not very 

 satisfactory. Breeding experiments on an exten- 

 sive scale can alone determine whether there is 

 in Partula a Mendelian segregation similar to 

 that described by Lang in Helix. The evidence 

 of the occurrence of mutations, also, other than* J 

 the dextral-sinistral mutation, which does not, as 1 1 

 a rule, help to differentiate species, is not by any^ 

 means conclusive. 



It seems quite possible that, with the wealth of 

 species, sub-species, and varieties which this 

 memoir reveals and illustrates, the conclu- 

 sion may be drawn that, after all, the genus Par- 

 tula may afford an example of the evolution of 

 species by the accumulation of small variations, 

 although the cause of this accumulation still- 

 remains a mystery. S. J. H. 



CONTINUATIVE EDUCATION AND ITS 

 OBJECTS. 



A COMMITTEE of Scottish teachers, chosen 

 from all branches of school education, has 

 recently issued a report entitled " Reform in 

 Scottish Education," ' which covers a wide field 

 and embraces a large variety of topics. Many of 

 the reforms advocated have already been set forth 

 by others, and, in particular, by the Workers'' 

 Educational Association. In common with the 

 latter body, the Scottish committee recommends 

 the raising of the leaving-school age of the primary 

 school to fifteen years ; the reduction of the size of 

 classes, so that every teacher shall have not more 

 than forty pupils under his charge at any one 

 time ; and the establishment of day continuation, 

 schools, to which all shall be compelled to go 

 from fifteen to eighteen, unless they are already in 

 attendance upon a course of secondary instruction. 

 The committee also demands the abolition of the 



1 Report «f the Scottish Education Re 'orm Committee. (34 North Bridge, 

 Edinburgh.) Price is. net. 



