CLASSIFICATION 417 



the type genus. For example, Colubrinae and Colubridae are the sub- 

 family and family of snakes of which Coluber is the type genus." 



Since evolution has become more or less of a keynote in the study of 

 Biology, it has been the desire of Biologists to group living structures 

 according to a common ancestry. This idea has been in the minds of 

 systematists since Darwin's time. 



Similarity of species of a given genus is supposed to indicate kinship, 

 so that the individuals among any given genus show greater diversity 

 than do the members of the species going to make up that genus, al- 

 though all members of the genus have something in common. We may 

 take as an example the vertebrates, which constitute the so-called highest 

 phylum, and the protozoa the single-celled animals which constitute 

 the so-called lowest phylum. Frogs being vertebrates, that is, having a 

 backbone, are classified in the same phylum as man, who also has a back- 

 bone, but there is much greater difference between a frog and a man than 

 there is between the many different species of frogs. 



As already stated, Systematists have usually used structure for their 

 important clue to affinities. "However, the evidential value of similarity 

 in one or several structures unaccompanied 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 liz- 

 ards (Amphisbaenidae), ( ), which closely resemble 

 certain snakes (Typhlopidae), ( ), in being blind, limb- 

 less, 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 only superficially similar. 

 In contrast with the early practice, the aim of taxonomists at the present 

 time is to group forms according to homology, which is considered an in- 

 dication 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 experimental breeding may all assist in establishing affini- 

 ties." 



It is, of course, necessary that before any final classification can be 

 made one must know the various forms that exist and have existed in the 

 past, and one of the greatest obstacles in this field is that most animals 

 having a soft body have decayed and left no record of themselves among 

 the fossil remains thus far found. Only those which possessed an in- 

 tensely hard substance, or lived and died in regions where, due to the 



