EVIDENCES FROM CLASSIFICATION 119 



structural characters is the chief clue to affinities. However, the 

 evidential value of similarity in one or several structures unaccom- 

 panied by the similarity of all parts is to be distrusted, since animals 

 widely separated and dissimilar in most characters may have certain 

 other features in common. Thus, the coots, phalaropes and grebes 

 among birds have lobate feet but, as indicated by other features, they 

 are not closely related; and there are certain lizards (Amphisbaenidae) 

 which closely resemble certain snakes (Typholopidae) in being blind, 

 limbless, and having a short tail. The early systematists were very 

 liable to bring together in their classification analogous forms, that is, 

 those which are functionally similar; or animals which are super- 

 ficially similar. In contrast with the early practice, the aim of 

 taxonomists at the present time is to group forms according to homol- 

 ogy, which is considered an indication of actual relationship. Since 

 a genetic classification must take into consideration the entire animal, 

 the search for affinities becomes an attempt to evaluate the results 

 of all morphological knowledge, and it is also becoming evident that 

 other things besides structure may throw light upon relationships. 

 The fossil records, geographical distribution, ecology and experi- 

 mental breeding may all assist in establishing affinities. 



The method of taxonomy. — It is evident that before the relation- 

 ships of animals can be determined the forms must be known, for 

 unknown forms constitute breaks in the pedigrees of the groups to 

 which they belong. Moreover, as pointed out above, the structural 

 characters, variation and distribution must be known before a form 

 can be placed in the proper place in a genetic system. For these 

 reasons an important part of systematic work is the description of 

 forms and an analysis of their differences. After the Linnaean 

 system was adopted zoologists attacked this virgin field and for many 

 years "species making" predominated. Even at the present time 

 when other aspects of zoology have come to receive relatively more 

 attention it is an interesting fact that the analytical method prevails 

 in systematic studies, and taxonomy suffers from, and in part merits, 

 the criticism that it is a mere cataloging of forms and ignores the 

 higher goal of investigation, namely, the discovery of the course of 

 evolution. Many systematists, however, recognize that the ultimate 

 purpose of taxonomic work is to discover the relationships as well as 

 the differences between the described forms in order that the course of 

 evolution may be determined. In other words, it is appreciated that 

 while analytical studies are necessary they are only preliminary, and 



