10 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 zodlogist 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 zodlogical 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 
