EXPERIMENTAL ZOOLOGY l8l 



his methods of work and some of the results already obtained ; 

 to contrast his attitude in approaching his problems with that 

 of perhaps the same man a quarter of a century ago; and, 

 finally, to state what this new attack is likely to mean for 

 zoology in particular and for human welfare and progress in 

 general. 



As indicating the extent to which experimental studies 

 have progressed, I may cite the titles given the principal 

 headings in Morgan's "Experimental Zoology," a recent book 

 dealing with work of this nature. Here may be found ac- 

 counts of the Experimental Study of Evolution, of Growth 

 and Regeneration, of Grafting, of the Influence of the Envi- 

 ronment, of the Determination of Sex, of the Appearence of 

 Secondary Sexual Characters, and to this list we may add, 

 Animal Behavior and the whole field of Experimental Em- 

 bryology which do not find a place in the volume mentioned. 



Most of these are topics which thirty years ago were 

 either not being seriously considered from the experimental 

 standpoint or in which the experimental method was only 

 beginning to be applied. Today, by a gathering up of scattered 

 records in earlier work and by the steady progress of experi- 

 mentation, we are in possession of a quite respectable body of 

 facts in each of the subjects named, and the work is being 

 so rapidly extended that the prospect of any one investigator's 

 knowing more than the net results in lines outside his own 

 is becoming discouraging. 



EXPERIMENTAL EMBRYOLOGY 



To illustrate the methods of work and some of the 

 results, let us now consider several of these topics in more 

 detail. A favorable one for this purpose is that of individual 

 development, first, because of its interest, and, second, because 

 the experimental embryologist has somewhat the start of his 

 fellows in other lines. 



