4zo 



THE QUARTERLY REVIEW OF BIOLOGY 



happen-if-I-should-do-thus-and-so type of 

 experiment); (2) the descriptive (Jormal- 

 analytische) experiment in which no re- 

 action is called forth in the object, (3) the 

 indefinite causal experiment and (4) the 

 causal-analytical experiment; — the latter 

 being the highest type. In 1889 Roux 

 was led to remark that "The causes of 

 organic formations (Gestaltungen) are at 

 present more unknown to us than the 

 causes of the movements of the heavenly 

 bodies were to mankind before Newton." 



Experimental embryology is thus, as 

 sciences go, very youthful — only forty- 

 five years of age — a veritable youngster, 

 and like all youngsters it is apt to be 

 intolerant. It is prone to assume a dis- 

 dainful attitude toward mere morphology, 

 and frequently implies that its achieve- 

 ments are of a higher order than those of 

 descriptive embryology. However, its 

 more thoughtful devotees realize that, 

 after all, there is but one science of em- 

 bryology; that description must precede 

 intelligent experiment and, furthermore, 

 that there are many aspects of develop- 

 ment that are not yet susceptible of ex- 

 perimental treatment. The importance 

 and the need of experimental analysis 

 must, however, be apparent to everyone. 



In the forty-five years since Roux's 

 experiment on the axes of the frog em- 

 bryo, a truly enormous mass of literature 

 dealing with experimental embryology has 

 accumulated. Each year sees an increase 

 in the production of literature over the pre- 

 ceding year, so numerous have workers in 

 the field become. As a result, it is difficult 

 for the beginner and even for the seasoned 

 worker to keep fully informed of the 

 current advances, and it becomes more and 

 more difficult for the novice to orient 

 himself in the subject. Summaries of 

 research programs and reviews of the 

 whole field from time to time are therefore 

 exceedingly valuable. 



In 1897 Professor Morgan published 

 The Development of the Frogs Egg. An 

 Introduction to Experimental Embryology. It 

 was an admirable work, the first of its kind 

 in the English language. At that time 

 Roux's Archiv fur Entwickelungs- 

 mechanik had been in existence only two 

 years and but five volumes had appeared, 

 and the Journal of Experimental Zoology 

 — to mention but two sources of publica- 

 tion — had not yet been founded. It was 

 then possible to give a very adequate 

 treatment of the subject, with particular 

 reference to the frog, in a volume of 192. 

 pages, including a 13 page bibliography. 



Since the appearance of Professor 

 Morgan's first summary, there have, of 

 course, been many important advances. 

 Since 1897 more than sixty volumes of 

 Roux's Archiv and fifty of the Journal of 

 Experimental Zoology have been issued. 

 Important research programs have been 

 initiated and prosecuted, in many in- 

 stances with gratifying success. To men- 

 tion only the most fruitful, one might cite: 

 (1) the important researches of Professor 

 Harrison on the growth of the nerve fiber, 

 his discovery of tissue culture and the 

 important series of analyses of the develop- 

 ment of the limb and other organs carried 

 out by himself and his students, (2) the 

 remarkable researches of Spemann and his 

 students on the Organi^ator" and the 

 determination of the various organs and 

 tissues of the Amphibian embryo, (3) the 

 studies of artificial parthenogenesis by 

 Loeb, Morgan, Bataillon, Brachet and 

 others, (4) studies on cell lineage by 

 Wilson, Conklin and others, (5) Child's 

 development of the theory of physiologi- 

 cal gradients, (6) the researches on cyto- 

 plasmic localizations by Conklin, Brachet 

 and others, and (7) the development of 

 the method of vital staining as employed 

 by Goodale, B. G. Smith, Vogt and 

 Goerttler in the study of the movements 



