THE ORDERS OF TELEOSTOMOUS FISHES 441 



of generations has elapsed which we may assume to be roughly- 

 equal along both lines of descent. Therefore, in degree of blood 

 kinship to this ancestral group both Bats and Insectivores are 

 about equally far removed. But in homological structural re- 

 semblances the modern Insectivores are much nearer to this 

 group than are the Bats, and hence so far as classification is 

 concerned, the ancestral group -and the Insectivores would 

 probably be placed in a single order, while the Bats are set off in 

 another order. Here plainly, degrees of blood relationship do not 

 exactly correspond to degrees of homological structural resemblances 

 and differences, nor to the divisions of classification. 



In order to make classification correspond even roughly to- 

 degrees of blood relationship, i.e. to phylogeny, we must assign 

 varying systematic values to different characters in proportion 

 to their inferred relative phylogenetic age. For example, the- 

 notochord and other chordate characters which appear in certain 

 larval Ascidians are regarded as of far greater phylogenetic age 

 than the typical characters of adult Ascidians, and hence these 

 transient characters are given a very high systematic value, so 

 that through them the group is placed within the phylum 

 Chordata. On the other hand neomorphs or "teleological" 

 characters are given much lower systematic values. The unique 

 sucking-disc of the Remoras, for example, which is believed to- 

 represent a modified spinous dorsal fin, 1 does not avail to remove 

 the family beyond the borders of the order Acanthopterygii. 

 In this way classification is roughly adjusted to phylogeny, but 

 the adjustment can never be complete or exact. 



These considerations reveal the general defects of both the 

 American and English methods of classification. The American 

 system may fail to emphasize the underlying affinities of struc- 

 turally well-defined groups, as, for example, of the Nematognathi 

 or Catfishes with the Plectospondyli or Characins and Carps. 

 The English system emphasizes the larger phylogenetic affinities 

 but may not give due value to the equally important structural 

 diversities. 



Again the English system seems to follow the general principle 



iR. Storms, "The Adhesive Disk of Echeneis," Ann. Mag. Nat. Hist., 

 (6) II, 1888, pp. 67-76. 



