September 23, 1904.] 



SCIENCE. 



401 



nor is it ever diminished or changed in the 

 slightest degree. 



Moreover, according to the current con- 

 ception, a changing species would common- 

 ly be modified into only one other form, or 

 at best become split into two different types, 

 separated from one another by flowering 

 at different seasons, or by some other evi- 

 dent means of isolation. My evening prim- 

 rose, however, produces in the same locality, 

 and at the same time, from the same group 

 of plants, quite a number of new forms, 

 diverging from their prototype in different 

 directions. 



Thence we must conclude that new spe- 

 cies are produced sideways by other forms, 

 and that this change only affects the prod- 

 uct, and not the producer. The same orig- 

 inal form can in this way give birth to 

 numerous others, and this single fact at 

 once gives an explanation of all those cases 

 in which species comprise numbers of sub- 

 species, or genera large series of nearly 

 allied forms. Numerous other distinct fea- 

 tures of our prevailing classification may 

 find on the same ground an easy and quite 

 natural explanation. 



To my mind, however, the real signifi- 

 cance of the new facts is not to be found 

 in the substitution of a new conception for 

 the now prevailing ideas ; it lies in the new 

 ways which it opens for scientific research. 

 The origin of species is no longer to be 

 considered as something beyond our experi- 

 ence. It reaches within the limits of direct 

 observation and experiment. Its only real 

 difficulty is the rarity of its occurrence ; 

 but this, of course, may be overcome by 

 persevering research. Mutability is mani- 

 festly an exceptional state of things if com- 

 pared with the ordinary constancy. But 

 it must occur in nature here and there, and 

 probably even in our immediate vicinity. 

 It has only to be sought for, and as soon 

 as this is done on a sufficiently large scale 



the study of the origin of species will be- 

 come an experimental science. 



New lines of work and new prospects 

 will then be opened, and the application of 

 new discoveries and new laws on forage 

 crops and industrial plants will largely re- 

 ward the patience and perseverance re- 

 quired by the present initial scientific 

 studies. Hugo Db Vries. 



SGIENTTFW BOOKS. 

 The Direction of Hair in Animals and Man. 

 By Walter Kidd, M.D., F.Z.S. London, 

 Adam and Charles Black. 1903. » 



Dr. Kidd's recent work on the ' Direction 

 of Hair in Animals and Man' is to a certain 

 extent a compilation of his numerous previous 

 works on the same general topic, to which is 

 added a considerable amount of theoretical 

 discussion. It is not intended to be an ex- 

 haustive treatment of the subject, but rather 

 a discussion of those particular conditions 

 which seem to substantiate the doctrines of 

 Lamarck. 



Three principles governing hair direction 

 are pointed out: 



1. That the simple and uniform hair slope 

 of primitive mammals (i. e., a general slope 

 from cephalic toward caudal extremity of the 

 body and from the proximal toward the distal 

 end of the limbs) is not easily departed from 

 in the individual development of any animal. 



2. That there are certain modifications in 

 this primitive arrangement that are due to 

 morphological changes in the animal exhibit- 

 ing them. 



3. That all of the remaining phenomena of 

 hair direction are to be explained by the 

 action of mechanical forces on the surface 

 of the body. 



The first of these principles receives a brief 

 discussion in which it is stated that the primi- 

 tive hair slope corresponds to the direction 

 of overlapping of the scales, which it is 'as- 

 sumed covered the bodies of the earliest mam- 

 mals. This law accounts for the slope of the 

 major part of the hairy covering of any mam- 

 mal. The existence of such a condition is 



