io Experimental Zoology 



more we know beforehand of the possible conditions that may 

 enter into the result. The ability of the experimenter is shown 

 in his insight into the possible factors that may be present. His 

 ability may be the result of a correct estimate of the possible 

 conditions, but for the highest order of work there is demanded 

 also great imaginative power. Good judgment and accurate 

 observation may lead to fine work, but constructive imagination 

 seems to be required for the highest order of original work. 

 This does not imply that accuracy of observation is not as requi- 

 site in original work as in descriptive and observational work, 

 and should always be expected; but the man who sees new 

 and overlooked combinations may open fields of research that 

 will set to work an army of able "investigators." 



The branches of biology that have made most extensive use 

 of the experimental method are physiology, bacteriology, and 

 physiological chemistry. The zoologist and the embryologist 

 have also to deal with physiological problems, and already the 

 beginning of important experimental work has been carried out 

 in this field ; but the most distinctive problem of zoological work is 

 the change in form that animals undergo, both in the course of 

 their development from the egg (embryology) and in their develop- 

 ment in time (evolution). It will be granted, I think, that these 

 formative problems are more difficult than those relating to 

 function with which the physiologist has concerned himself in 

 the main; but this is all the greater reason why the experimental 

 method should be used in their study, especially after so much 

 purely descriptive work has been already done. 



The term " morphology " has been used in recent times to 

 denote the study of form, as contrasted with physiology, that 

 deals with functional changes. Morphogenesis has also been 

 employed to signify a study of the changes in form through 

 which organisms pass. It is mainly the experimental study of 

 these changes in form that I propose to examine in the follow- 

 ing pages. Experimental morphology would perhaps nearly 

 indicate the field to be examined ; but since the line between 

 experimental physiology and experimental morphology is often 



