xlii Journal of Comparative^Neurology. 



simply by the Cox method are greatly enhanced m value by the pot- 

 ash treatment. The finest details of structure which have hitherto 

 been revealed by the mercury and silver-chrome methods are beauti- 

 fully brought out by this means. Nor do I know any process which 

 can compete with it for wealth of structure and beauty of delineation. 

 We sacrifice, it is true, the rapidity of other methods of preparation, 

 but this is greatly counterbalanced by the certainty of results which 

 appear to be ensured by Cox's fluid, and the far greater beauty of the 

 sections. Sublimate preparations were at one time proverbially uncer- 

 tain in results ; the potash treatment of sections, prepared as above 

 described, is open to no such criticism. It was stated m the earlier 

 note that liquor ammonise is ruinous to the silver-chrome preparation 

 (chromate of silver being soluble in excess of ammonia); this is not 

 so in the sublimate preparations. Solutions of potash, soda, or am- 

 monia may be used, thought I give preference to the former." 



Darwin and after Darwin, Yol. III.' 



This concluding volume, -like the second one of the same series, 

 was left unfinished at the time of the author's death. The most im- 

 portant parts of the work were, however, already in type and we may 

 rest assured that these pages accurately represent his most mature 

 thoughts upon the questions discussed. This is undoubtely the most 

 important volume of the three, for it is here that Mr. Romanes' most 

 valuable direct contributions to the theory of evolution are found. 

 The dominant note is indicated by the sub-title. Isolation, and by this 

 is meant simply the prevention of intercrossing, Weismann's Amixia. 

 The barriers are of various kinds, geographical, physiological, etc., 

 and the isolation maybe Indiscriminate, i. e., without reference to the 

 resemblances of the separated individuals to one another, or Discrim- 

 inate, i. e., the separation of a group of individuals on the basis of 

 certain distinguishing characters which they have in common. Indis- 

 criminate isolation has no special evolutionary significance, except in 

 so far as it tends to pass into the discriminate type. But discriminate 

 isolation is shown to be of the most fundamental importance ; indeed 

 according to Romanes' view it is more fundamental than natural selec- 

 tion itself in that the latter is but a mode of isolation in which the 

 isolation is with reference to superiority or fitness and is effected by 



' George John Romanes. Darwin and after Darwin. III. Post-Dar- 

 winian Questions. Isolation and Physiological Selection. Edited by Prof. C. 

 Lloyd Morgan. Chicago: The Open Court Publishing Co., 1897. Cloth, $1.00. 



