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SCIENCE. 



LN. S. Vol. IV. No. 85. 



assurance tliat this is not a primitive un- 

 gulate character retained in these two series 

 and lost in the others. Having recovered 

 the various extinct genera of both these 

 phyla, we may trace out the gradual trans- 

 formation of the humerus and definitely 

 show that the resemblance has been inde- 

 pendently acquired at a comparatively late 

 period, and is not a case of a persistent 

 primitive feature. 



In short, the difficultj^ of reaching firmly 

 fixed conclusions upon questions of homol- 

 ogy and relationship by the exclusive use 

 of comparative anatomy lies in the fact, 

 that this method deals only with the 

 modern assemblage of animals, a mere frag- 

 ment of that which has existed in former 

 times. It is like attempting to work out 

 the etymology of a language which has no 

 literature to register its changes. 



The second method of morphological in- 

 quiry, embryology, has had a somewhat 

 chequered career. Not many years ago it 

 was universally regarded as the infallible 

 test of morphological theory, and the prin- 

 ciple that the ontogeny repeated the phylo- 

 genetic history in abbreviated form was ac- 

 cepted, almost without question, as a fund- 

 amental law. But this view has fallen 

 somewhat into discredit. The admission 

 which very early had to be made, that 

 '■ cenogenetic ' features of development were 

 imposed upon or substituted for those due 

 to ancestral inheritance, opened the door to 

 an unduly subjective way of dealing with 

 embry ©logical evidence and deprived the 

 method of that authoritative character 

 which had so generally been ascribed to it. 

 ISTow the whole recapitulation theory is 

 boldly called in question, and, in the ad- 

 mirable lecture delivered last year in this 

 place, Prof. E. B. Wilson showed the un- 

 trustworthy nature of the embryological 

 criterion of homology. The difficulty in 

 this case lies in the absence of any ' canons 

 of interpretation ' (to use Bateson's phrase) 



by which the contradictory data of embry- 

 ology may be harmonized into a consistent 

 whole. To take a concrete illustration : 

 The ontogenetic development of the horse's 

 teeth would give us a very inadequate and 

 indeed false conception of the actual steps 

 of change, by which the modern type of 

 dentition has been attained, nor would 

 embryology show that the horse is de- 

 scended from five-toed ancestors. Know- 

 ing, as we do from the fossils, the phyletic 

 series, the embryological facts may be 

 readily understood. It is an undue reliance 

 upon such facts which has led to the con- 

 crescence theory of tooth development, now 

 so rife in Germany and which seems so 

 absurd when viewed in the light of paleon- 

 tology. 



I have no intention of belittling the 

 splendid services which embryology has 

 rendered to morphology, but merely to 

 point out that this method alone cannot 

 reach finality any better tlian comparative 

 anatomy. It resembles dealing with a lit- 

 erature that has been vitiated by many for- 

 geries, only the grossest and most palpable 

 of which can be readily detected. 



A third method of attacking morphologi- 

 cal problems is that offered hj paleontology. 

 Let us begin our consideration of this 

 method hy frankly acknowledging its draw- 

 backs and limitations. (1) In the first 

 place there is the imperfection of the geo- 

 logical record. Paleontology does not pro- 

 fess and never can hope to reconstruct the 

 whole history of life upon the earth, or even 

 the greater part of that history ; very many 

 chapters are irretrievably lost, and others 

 are so fragmentary that they teach us little 

 or nothing. The great sedimentary de- 

 posits which contain nearly the whole re- 

 corded history of the globe were laid down 

 under water, and for a land animal or plant 

 to be entombed there is a lucky accident. 

 If all we could learn of the terrestrial life of 

 North America had to be deciphered from 



