EVIDENCES FROM CLASSIFICATION I19Q 
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.—lIt 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 zodlogists attacked this virgin field and for many 
years ‘“‘species making” predominated. Even at the present time 
when other aspects of zodlogy 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 
