Apkil 9, 1915] 



SCIENCE 



535 



fessor MacBride; he stands firmly by the de- 

 scriptive method, and the phylogenetic point 

 of view as fundamental. All else is secondary : 

 " It is, therefore, of the essence of comparative 

 embryology to separate the fundamental an- 

 cestral traits of development from the super- 

 ficial and secondary, and this is the task that 

 has been patiently pursued for the last thirty 

 years." If the results are considered disap- 

 pointing, this is due largely to the human fail- 

 ing of lack of patience; and if divergences of 

 opinion with reference to phylogenetic prob- 

 lems seem irreconcilable, in what better posi- 

 tion are the adherents of the experimental 

 analytical school? Are not opinions equally 

 diverse and irreconcilable there ? " The real 

 truth is that experimental embryology is an 

 adjunct and not an alternative to comparative 

 embryology." 



As good an illustration of the author's pre- 

 ferred form of generalization as the book af- 

 fords is contained in the following quotation : 



"We are thus led to form the following con- 

 ception of the past history of the lower Meta- 

 zoa. A widespread and dominant race of 

 blastula-like animals once swarmed in the 

 primeval seas. Some of these took to a creep- 

 ing life and eventually gave rise to the group of 

 sponges ; others kept to the free-swimming life 

 and developed into planulffi, and so gave rise 

 to the Ooelenterata. Some of these planulas, by 

 the specialization of the cilia into comblike 

 locomotor organs, became Otenophora; whilst 

 the remainder adopted a fixed life and at- 

 tached themselves by their aboral poles. This 

 change occurred in the different divisions of the 

 stock at different stages of the evolution of the 

 internal organs of the planula ancestor, and 

 in this way the groups of Hydrozoa, Scypho- 

 zoa and Actinozoa arose." 



One is tempted to ask are such questions 

 really the fundamental questions of compara- 

 tive embryology? No one doubts the broad 

 fact of evolution; nor can it be questioned 

 that embryology is a strong aid to compara- 

 tive anatomy and paleontology in the investi- 

 gations of relationships. But the method has 

 its limits, which seem to be surpassed in the 

 above citation. 



The experimental method in embryology is 

 not a mere adjunct to comparative embryology 

 of this sort. Indeed, experimental embryology 

 has contributed very little to the phylogenetic 

 interpretation of ontogeny, and in the very na- 

 ture of things it is impossible that it should 

 do so. 



We have in fact two quite radically distinct 

 points of view in embryology, viz. : the com- 

 parative anatomical and phylogenetic repre- 

 sented by Professor MacBride, and the func- 

 tional analytic. Both rest, of course, upon 

 descriptive embryology. Experimental meth- 

 ods are more or less applicable to both. But 

 whereas their use for phylogenetic purposes 

 must be limited to relatively simple purposes, 

 such as determination of origins of parts where 

 purely observational method fails, and can be 

 of no service for the more general problems of 

 phylogeny, experimental methods contribute 

 the essential data for functional analytic prob- 

 lems of embryology, and are absolutely neces- 

 sary for the investigation of all the more 

 fundamental questions. 



The phylogenetic and the functional an- 

 alytic points of view in embryology diverge 

 from a common basis of observation and ex- 

 periment. Experimental embryology is not 

 merely an adjunct to comparative embryology. 

 The broadest aspects of phylogenetic embryol- 

 ogy must forever, so far as we can see, re- 

 main matters of opinion, which can never be 

 subjected to crucial experimental investiga- 

 tion. The reaction against this type of em- 

 bryological research is therefore due not 

 merely to lack of patience, but also to lack of 

 confidence. That there remains much impor- 

 tant work to be done of a purely descriptive 

 character in embryology goes without saying; 

 it is being produced all the time; but in the 

 best works of recent years there is a notable 

 reserve with reference to phylogenetic specula- 

 tion. 



Professor MacBride has selected and limited 

 his material according to his point of view. 

 One result is an altogether inadequate treat- 

 ment of general and also experimental embry- 

 ology. In this there is no lack of consistency, 

 and it is therefore not in itself a matter for 



