Vol. XXI 

 iqo4 



J Von Ihering, Biology of the Tyrannidce. 3^7 



guished by the most brilliant colors of brown, red, blue, and green. 

 It is true that the Pici, Psittaci, and other birds that lay their eggs 

 in hollow trees, all have white eggs, but eggs of the same color 

 are found also in the open nests of the Trochilidae and of the 

 Columbae. Returning to the Tyrannidae we find the o.g'g of Mac/ie- 

 tornis rixosa wholly different from those of the true Taeniopterinae, 

 and resembling in its numerous, large, somewhat elongated brown- 

 ish spots the eggs of the genera Empidonomus and Myiarchus, 

 especially those of the latter. These facts throw doubt on the 

 correctness of the generally accepted systematic position of Mache- 

 tornis. So far as regards the egg of Tyranmis aurantioatronotatus 

 Lafr. «Sc D'Orb., it belongs to the genus Tyramius and not to 

 EmpidoJiomus. 



These differences, therefore, cannot be explained by the so- 

 called law of 'natural selection,' but bear relations to the genetic 

 affinities and the inner movements which, independently of the 

 supposed ' natural selection,' determined the individual variation 

 as well as the phylogenetic development of the organisms. 



After what I have stated it is evident that the systematic 

 arrangement of the Tyrannidae in its present form can only be 

 considered as provisional, and it may be well altered when a gen- 

 eral anatomical study of the whole group has been made. At 

 present the systematic sections are only based on a restricted 

 number of external characters, principally on the form of the 

 tarsi, feet and bills. These characters are in intimate connection 

 with the manner of life. In this way we are exposed to the 

 danger of confounding essential typical characters with adaptive 

 ones. I think that such a mistake took place on the occasion of 

 the formation of the subfamily Taeniopterinae. This section 

 embraces forms with strong feet, strong and elongated tarsi, and 

 slender elongated bills, characters which seem to result from the 

 life on the ground on the pampas and campos, which these birds 

 inhabit. 



In general this subfamily may be considered a very natural 

 one. The predominant colors of the species are gray, white, and 

 black. These colors are not common in the family Tyrannidae as 

 a whole, and they are evidently to be considered as being acquired 

 characters and not of a phylogenetic value. This is proved by 



