phology since 1859 has been documenting the phylogenetic his- 

 tory of structural elements, which is a purely descriptive operation, 

 its proper goal as a science is to explain the structural stages which 

 organisms have passed through in the course of time in terms of 

 their genetic origin and environmental selection. It is the author's 

 opinion that comparative morphologists can for some time yet 

 legitimately confine themselves to phylogenetic studies and inter- 

 pretations. This is by no means a "purely descriptive" activity 

 nor a matter of documenting a preconceived pattern of evolution, 

 but rather the discovery of the actual, or most probable, pathways 

 that have been followed. Thus, this area of scholarly endeavor is 

 not in competition with genetics or ecology but complements 

 these by supplying phylogenetic sequences for analysis. 



Comparative morphology is not an experimental study; it is 

 primarily a descriptive and interpretive realm. This does not pre- 

 clude the possibility of experimental work; it implies that the usual 

 activity is one of determining taxonomic groups and revealing the 

 morphological time series behind them. Thus the comparative 

 morphologist is either a taxonomist dealing with some living group 

 or a palaeontologist using the phylogeny of fossil animals to re- 

 veal the ages of rock strata. The geneticist, ecologist, or physiologist 

 may use comparative morphology as a part of his research back- 

 ground, just as the comparative morphologist utilizes knowledge 

 of embryology, genetics, physiology, and ecology in pursuit of the 

 history of a structure. 



The basic prerequisite for study in this field is a patient, meticu- 

 lous, detail-seeking nature. All ideas must be carefully screened 

 and tested both in terms of direct observations and of historical 

 retrospect. Yet one must, like a detective, continually re-sort the 

 evidence with the hope of discovering its hidden significance. One 

 cannot expect simple, direct, or quantitatively expressed answers, 

 but only the most indirect "revelations." Technological skills may 

 also be important in a study involving dissection and the prepara- 

 tion of many kinds of specimens from serial sections of embryos to 

 the uncovering of a fossil from its stony shroud. There are many 

 pitfalls and temptations inherent in the methods of this study and 

 one should continually return to the instructions of Louis Agassiz 

 — study nature and not books. 



In the preparation of this text, I have received help from a num- 

 ber of sources. I wish to express my thanks to Dr. Peter Gray, the 

 consulting editor for Reinhold Books in the Biological Sciences, 

 for his advice and encouragement. Miss Joan Thomas assisted 

 with the illustrations, along with several student assistants. Mr. 



