Classification 419 



another author. The name of a subfamily is formed by adding the 

 ending inae, and the name of a family by adding idae to the root of the 

 name of the type genus. For example, Colubrinae and Colubridae are 

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



Since evolution has become more or less 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 kin- 

 ship, so that the individuals among any given genus show greater 

 diversity than do the members of the species going to make up that 

 genus, although 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 backbone, 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," again quoting Professor Schull, 

 "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 



(Typhlopidae), ( ), 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 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 indication of actual relationship. Since a genetic classifi- 

 cation 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, geo- 

 graphical distribution, ecology, and experimental breeding may all assist 

 in establishing affinities." 



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 



