E\TDEXCES FROM CL-\SSinCATION II9 



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

 e\idential value of similarity in one or 5e%"eral structiires unaccom- 

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

 -R-idely 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 (Tj'pholopidae) in being blind, 

 limbless, and ha^•ing a short tail. The early sj^stematists 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, ecolog>' and experi- 

 mental breeding may all assist in estaijlishing affinities. 



The method of taxonomy. — It is e\'ident that before the relation- 

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

 unknown forms constitute breaks in the p>edigrees of the groups to 

 which they belong, itioreover, as pointed out above, the structural 

 characters, variation and distribution must be known before a form 

 can be plax:ed in the proper place in a genetic system. For these 

 reasons an important part of systematic work is the description of 

 forms and an anal>-sis of their differences. After the Linnaean 

 system was adopted zoologists attacked this \-irgin field and for many 

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

 when other aspects of zoologj.' have come to receive relatively more 

 attention it is an interesting fact that the anal3^ical 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 

 e^'olution. Many systematists, howe\'er, 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 anah-tical studies are necessary' they are only preliminary^ and 



