October 21, 1904.] 



SCIENCE. 



535 



tain convenience of description. Moreover, 

 the acceptance of this compromise must not 

 be understood to grant free license to argue 

 from one to another of the forms included, 

 as though they were equivalents ; what has 

 resulted in one line of descent can at best 

 only throw a side light on what has hap- 

 pened in another distinct line, and in pro- 

 portion as the lines involved in a com- 

 parison are more remote from one another, 

 their comparison assumes more and more 

 the character of a mere analogy. The dan- 

 ger which our compromise brings with it is 

 that this will not be clearly kept in mind. 

 At all hazards the strict phyletic view 

 should underlie all present morphological 

 discussion, notwithstanding that, for mere 

 convenience, that view may not be clearly 

 reflected in the classification of the parts. 

 This makes me hope that the compromise is 

 only a temporary concession, and that it 

 will give way ultimately to the demands 

 which a more detailed knowledge of descent 

 is sure to bring. 



It is well, however, in connection with 

 discussions such as these, to impress upon 

 the lay public that all evolutionary theories 

 are, like other scientific theories, hypoth- 

 eses incapable of complete proof. No one 

 will appreciate this more fully than biolog- 

 ical investigators themselves, for they are 

 in the best position to know how insuffi- 

 cient the evidence actually is, and how 

 liberal a use has to be made of the imagin- 

 ation in bridging over the wide gaps in the 

 series of known forms. The details of a 

 story thus constructed depend so largely 

 on comparative opinion, and in so slight a 

 degree on positive demonstration, that the 

 history as told by competent experts in 

 comparative morphology may vary in ma- 

 terial features. A little more Aveight al- 

 lowed for certain observed details, or a 

 little less for others, will be sufficient to dis- 

 turb the balance of the evidence derived 

 from a wide area of fact, and consequently 



to distort the historical picture. There 

 is in truth no finality in discussions on the 

 genesis and progress of -organic life, or in 

 the kaleidoscopic changes of opinion, since 

 any new fact of importance will in some 

 degree affect the weight accorded to 

 others, and may vary the general result. It 

 will be objected that conclusions which are 

 so plastic are little better than expressions 

 of personal taste ; that the study of compar- 

 ative morphology, is, therefore, calculated 

 to dishearten its votaries, while the non- 

 specialist public, which is compelled to take 

 its information at second hand, will be be- 

 wildered, and will conclude that it is use- 

 less to pursue a subject which shows so 

 little stability. But, on the other hand, 

 those who follow the progress of morphol- 

 ogy with sympathetic care will take heart 

 when they compare its present position 

 with that of a generation ag'o ; it is en- 

 couraging to think that it is little more 

 than half a century since the history of the 

 life cycle of a fern was first completed. 

 In some sixty years a vast array of kin- 

 dred facts has been acquired, and a 

 theoretic structure is being raised upon 

 them which, though still protean, is grad- 

 ually__acquiring some settled form. Never 

 has the advance of morphological thought 

 been more rapid than at present. The sup- 

 port of the facts of alternation from the 

 unexpected quarter of minute cytology 

 has been one of the most striking features 

 in the recent history of our science. The 

 discovery of spermatozoids in the cycads 

 and Gingkoacese has filled in a gap in the 

 story of evolution which all followers of 

 Hof meister must have felt. But in no field 

 of morphological research has investigation 

 been more amply rewarded than in paleo- 

 phytology. The luminous facts derived 

 from fossils are shedding fresh light on 

 obscure problems, such as the origin of the 

 seed habit, and helping us to locate such 

 difficult groups as the Psilotacese and 



