NA TURE 



[December 5, 1907 



regeneration, the relation of regeneration to nutrition, 

 to reproduction, to age, and to environmental condi- 

 tions. The author's exposition is lucid, and there is 

 an illustration on every second page. In the second 

 part of the book we find an account of grafting or 

 transplantation in plants and in animals, with strange 

 figures of grafted polyps and worms, pupje and tad- 

 poles, frogs and newts — an altogether quaint assem- 

 blage. At the end of the book there is an exhaustive 

 bibliography, certainly amazing in its dimensions, very 

 usefully subdivided into sections relating to different 

 aspects of the subject. .As to the general theory of 

 regeneration, Prof. Korschelt seems to incline to a 

 compromise between the views of Weismann and 

 Morgan, admitting that there is a great deal to be 

 said on both sides. He seems — for he is anything but 

 dogmatic — to believe that the regenerative capacity is 

 a primary quality of living matter, which, along cer- 

 tain lines of evolution, has been accentuated and 

 specialised by natural selection. Thus the regenerative 

 capacity is, in general, a primary quality, but in parti- 

 cular cases an adaptive character. 

 Organische Zweckmcissigkeit, Entivickliing und 



Vercrhung von Standpiinkte der Physiologie. By Dr. 



Paul Jensen. Pp. xiii + 251. (Jena: Gustav Fischer, 



1907.) Price 5 marks. 

 Prof. Je.nsen has produced a book which attempts to 

 deal in a philosophical manner with some of the most 

 difficult problems that confront the biologist. The 

 reader will perhaps be inclined to deprecate an attitude 

 of " cock-sureness " that rather pervades the whole, 

 but he will at the same time recognise that in many 

 places the author is stimulating and suggestive. 



A great part of the whole volume is devoted to the 

 examination of the various explanations that have been 

 put forward to account for adaptation in the organic 

 world, as well as of those which have attempted to 

 deal with the meaning and the method of evolution. 



After a somewhat lengthy discussion of these topics, 

 the author puts forward the analogies shown bv 

 various cosmic mechanisms to assume positions of 

 relative or absolute stability, and he regards them as 

 useful in throwing light on the problems of evolution. 

 The whole of the constructive part of the book strikes 

 us as very speculative, and though of undoubted in- 

 terest, it may be doubted whether the point of view- 

 as advocated by Jensen will find much sympathy 

 amongst working biologists. The title of the work 

 indicates that it is written from the standpoint of 

 physiology, but we have searched its pages in vain to 

 find any serious physiology, as ordinarily understood, 

 discussed in it at all. There is much philosophy of a 

 sort, and much acute destructive criticism of many 

 ideas and notions that are widely current. But it does 

 not appear that in grappling with the problems he has 

 set himself to face and to solve, the author has 

 expressed himself so clearly as did Herbert Spencer 

 many years ago. There is much in the work before 

 us that recalls the " Principles of Biology," though 

 there is a great difference between the lucid expression 

 of Herbert Spencer and that of our author. The fol- 

 lowing passage, relating to the causes of extinction 

 of species and genera in the past, will furnish a fair 

 sample of the method of treatment : — " According to 

 our theory of development, a natural extinction of 

 species is to be anticipated as the expression of a 

 general law. Organisms that are dying out in this 

 way fall into the same category as those systems 

 which, after enduring through a long period in a 

 stationary condition, pass finally, as the result of slowly 

 advancing changes, into a relatively stable state 

 (death); a destiny that ... in time will overtake many 

 existing org.-inisms, in spite of the ' rejuvenating ' 

 effects of amphimixis " (p. 237). J. B. F. 



NO 1988, VOL. yyl 



LETTERS TO THE EDITOR. 

 [The Editor does not hold himself responsibte for opinions 

 expressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part of Nature. 

 No notice is taken of anonymous communications.] 



The Windings of Rivers. 



At the meeting of tlie British Association at Edinburgh 

 in 1892 I read a paper on the subject of the winding of 

 rivers before the geographical section. It was illustrated 

 by a large number of diagrams, but, as these could not 

 be included in the report of the meeting, only the title of 

 the paper appeared. It may not be out of place to give 

 a short account of it, as the subject is now attracting 

 some attention. 



In Fig. I the courses of three streams are shown. 

 These are distinguished by the letters A, B, C, without 

 indication of their identity or of the scale on which they 

 are drawn. If anyone were to try to select the one which 

 represents the largest or the smallest of these streams he 

 might do so correctly, but he would not be surprised if 

 he were told that he had guessed wrongly, for it could 

 only be a guess. The length of each tracing is the same. 

 In nature it represents in A nine English miles, in B 

 two hundred and sixteen miles, and in C one and a half 

 miles. 



Tracing B represents the part of the Mississippi between 

 the mouth of the Arkansas River and that of the Re I 

 River. Tracing A represents the Devon Water, a tribu- 

 tary of the Forth, and tracing C represents a quite in 

 significant brook called the Catter Burn, a tributary of the 

 Endrick, one of the principal affluents of Loch Lomond. 

 These tracings, and indeed the maps of all countries, 

 show clearly the great family likeness exhibited by rivers 

 in all parts of the world. This likeness rests on the fact 

 that in all rivers the relation between the length of an 

 arc or bow and that of its chord is nearly the same. It is 

 an organic rather than a family likeness, and resembles 

 that which exists between dogs of different breeds or 

 builds. 



The following table shows, for a selection of well-known 

 rivers, the degree in which the above relation holds 



From the table it will be seen that over a length of 

 nearly one thousand miles of the Mississippi the average 

 length of stream, following the windings, is 172 times 

 greater than the direct distance. In the Lahn we find 



