330 COMPARATIVE ANATOMY 



and ontogenetic routes, or not at all, that we must make the passage 

 from phylum to phylum, we are bound to do the best we can with 

 the data we have. 



One experienced with some of the problems in this field, and like- 

 wise acquainted with its literature, must be impressed by the lack 

 of general guiding principles of procedure; and especially by the 

 lack of criteria for estimating the value of evidence. Several bio- 

 logists have felt this, and have made praiseworthy attempts to fill 

 the needs. Among these should be especially mentioned Gegen- 

 baur, Cope, Dohrn, E. B. Wilson, Montgomery, and Gaskell. I 

 desire to devote some attention to this topic. The time being so 

 limited as to make it impossible to treat it with any measure of 

 fullness, I merely pick out some of the points that seem to me of 

 most immediate importance for the present state of progress, and 

 tendencies without special regard to their logical order or their 

 coherence. 



(a) My first point is one of professional delimitation, and attitude 

 of mind, rather than of general biological principles. I state it thus: 

 We must cease to be embryologists as distinguished from anatomists 

 when it comes to any particular problem of affinities between 

 groups of animals. Montgomery (1902, p. 225) has recently said: 

 "As to which of these methods is the more correct has been and 

 probably will continue to be a question of dispute. The compara- 

 tive anatomists maintain one side, the embryologists another, and 

 probably because the former are less conversant with the facts of 

 embryology, and the latter with the facts of adult structure." I 

 suppose this statement of the present attitude of embryologists and 

 anatomists toward one another is true; and I am absolutely sure 

 that so long as it is, we shall not touch solid ground for our general 

 conclusions. What I would insist on is that there is no sufficient 

 reason why it should be so. 



True, no one can compass in his personal investigations the whole 

 range of both embryology and comparative anatomy, but that is 

 in no wise essential. All that is necessary is to redraw our lines of 

 specialization. Instead of drawing them around masses of facts 

 and through problems, as is so frequently done, they must be drawn 

 around problems, and through, if necessary, masses of data. There 

 is no reason why a zoologist should come to what he would regard 

 as a final opinion on the relationship, for example, of the mollusca 

 and annelida without having himself examined with equal thorough- 

 ness the facts of both anatomy and embryology bearing upon the 

 question. 



Having reached a position where we might use the facts of devel- 

 opment and adult structure with equal facility and equal favor, 

 we should certainly find that in nearly every problem of phylogeny 



