NO. 



TELEOSTEAN FISHES — GOSLINE 



Second, all four features show a progressive change from the basal 

 clupeiform fishes to the percoids. Frequently the nature of the change 

 that occurs between the basal members of different orders is of the 

 same type as that occurring between the more "primitive" and more 

 "advanced" members of a single order (though this is by no means 

 always true). Under the circumstances it seems well to point out that 

 the successive levels of organization found in a structure can have 

 evolved in two quite different ways (diagram i). At the left, four 



Q 







□ 



n 



Diagram i. 



levels of structural organization are represented as having arisen 

 through a single father-son lineage ; at the right, these same levels are 

 shown as having developed through parallel changes occurring to 

 different degrees in different lineages. In short, similar or successive 

 levels of structural organization in any one character may or may not 

 be indicative of genetic relationships, depending, among other things, 

 on whether the similarities have been developed by the means indi- 

 cated at the left or at the right of the diagram. 



I. THE CAUDAL SKELETON 



The caudal skeleton of teleostean fishes has been the subject of a 

 number of investigations, but no very coherent picture of the evolu- 

 tion of this structure in teleosts has materialized. There are a number 

 of reasons for this, one being that the forms with a specialized 

 caudal skeleton, e.g., the cods, have received a large proportion of the 

 attention. The resulting impression is one of kaleidoscopic permuta- 

 tions brought about by losses and fusions. If, however, the basal 



