386 THE EVOLUTION OF LIFE. 



bearing fibres, each of whicli again bears a fringe of down. 

 But in some birds, as in the ostrich, various stages of arrested 

 development of the feathers may be traced ; beginning with 

 the unusually-elaborated feathers of the tail, and ending with 

 those about the beak, which are reduced to simple hairs. Nor 

 is this the extreme case. In the Apteryo: we see the whole 

 of the feathers Teduced t" a hair-like form. Again, the hair 

 which commonly covers the body in mammals, is compara- 

 tively rudimentary over the greater part of the human body, 

 and is in some parts reduced to mere down — down which 

 nevertheless proves itself to be homologous with the hair of 

 mammals ia general, by occasionally developing into the 

 original form.. JSTumerous cases of aborted organs are given 

 by JVIr Darwin, of which a few may be here added. " I^o- 

 thing can be plainer," he remarks, "than that wings are formed 

 for flight, yet in how many insects do we see wings so reduced 

 in size as to be utterly incapable of flight, and not rarely 

 lying under wing-cases, firmly soldered together?" * * * 

 " In plants vith separated sexes, the male flowers often have 

 a rudiment of a pistil ; and Holreuter found that by crossing 

 such male plants with an hermaphrodite species, the rudi- 

 ment of the pistil in the hybrid ofispring was much increased 

 in size ; and this shows that the rudiment and the perfect pistil 

 are essentially aKlie in nature." And then, to complete the 

 proof that these undeveloped parts are marks of descent from 

 races in which they were developed, there are not a few direct 

 experiences of this relation. " We have plenty of cases of 

 rudimentary organs in our domestic productions — as the 

 stump of a tail in tailless breeds — ^the vestige of an ear in 

 earless breeds — the re-appearance of minute dangling horns 

 in hornless breeds of cattle." 



Here, as before, the teleological doctrine fails utterly ; 

 for these rudimentary organs are useless, and occasionally 

 even detrimental. The doctrine of typical plans is equally 

 out of court ; for while, in some members of a group, rudi- 

 mentary organs completing the general tj'pe are traceable, 



