144 



SCIENCE. 



[N. S. Vol. XVI. No. 395. 



New York and Maine. He will be as- 

 sisted by Mr. E. M. Kindle. 



Mr. Bailey Willis will continue the 

 supervision of the investigations in areal 

 and stratigraphic geology. He will visit 

 field parties in various parts of the United 

 States and will investigate the stratig- 

 raphy along the eastern base of the Rocky 

 ]\Iountains in JMontana and Wyoming. 



Professor J. E. Wolff will continue the 

 investigation of the areal and structural 

 geology in the crystalline areas of New 

 Jersey and southern Vermont. 



July 12, 1902. 



SCIENTIFIC BOOKS. 



Lehrhuch der vergleichenden EntivicMungs- 

 ■geschichte der wirbellosen Thiere. Allge-- 

 meiuer Theil. Erste-Lieferung. Erste und 

 Zweite Auflage. By E. Korschelt aud K. 

 Heider. Jena, Gustav Fischer. 1902. 

 Pp. s-f538; 318* figs. 



Wlien the third and final instalment of the 

 'special part' of the 'Lehrbuch der vergleich- 

 enden Entwieklungsgeschichte der wirbellosen 

 Thiere,' by Professors Korschelt and Heider, 

 made its appearance, zoologists who had the 

 good fortune to be familiar with the work 

 began to look forward with no little eagerness 

 to the appearance of the 'general part.' It 

 was, however, a case of hope long deferred, but 

 now, after a lapse of nine years, expectations 

 are in the way of being fulfilled. Our knowl- 

 edge of the embryology of the invertebrates 

 has increased greatly in the interval and a 

 demand has arisen for a new edition of the 

 'special part,' but the authors, feeling that they 

 were still in debt to the public to the extent 

 of the general jsart, have decided to complete 

 the work as originally planned before begin- 

 ning a revision. As a result we have now 

 before us a first instalment of the 'general 

 part,' which is at once an earnest for the com- 

 pletion of the first edition and the beginning 

 of the second. 



Zoologists will find, however, for the loss 

 resulting from the long postponement of the 

 volume, ample compensation in the greater 



thoroughness with which it is now possible to 

 discuss the general problems of development. 

 In the last decade the standpoint from which 

 these problems are regarded has shifted 

 greatly; the mountain tops, from which they 

 were formerly seen but dimly, have been left 

 behind and we are now upon the nearer plains, 

 with numerous difficulties, it is true, still to be 

 overcome, but with the advantage that we have 

 come into actual contact with them and can, 

 at close range, lay our plans for their sur- 

 mounting. And that this is the case is largely 

 due to the results obtained from experimental 

 embryology. 



In the present volume will be found one of 

 the clearest and fullest statements of the re- 

 sults and aims of this department of investi- 

 gation which has yet been presented. The 

 first three chapters or almost half the volume 

 is devoted to it, the first chapter, after a brief 

 introduction discussing the influence of ex- 

 ternal stimuli on development ; the second, the 

 determination problem; and the third, the 

 effects of internal factors.- To one familiar 

 with the 'special part' of the work it will 

 suffice to say that the facts are presented in 

 the present volume with the same wealth of 

 detail and clearness of exposition that charac- 

 terized the earlier volumes and to these there is 

 again added a critical and judicious estimate 

 of the value of the facts. The authors have 

 carefully avoided the advocacy of extreme posi- 

 tions and have maintained throughout what 

 may be termed a broadly conservative attitude, 

 compared with views which have been pro- 

 mulgated by some recent writers. It is im- 

 Ijossible to discuss here in detail the various 

 topics considered in the volume, but a few quo- 

 tations may not be out of place to indicate the 

 standpoint of the authors on some of the more 

 general problems which confront us. 



"It results from this that we err in en- 

 deavoring to give a general answer to the ques- 

 tion whether it is preformation or epigenesis 

 which controls the phenomena of development. 

 We must particularize and endeavor by ex- 

 periment to answer this question for each 

 individual stage and each form. It will be 

 found that in many cases the development of 

 a certain organ or some morphological relation 



