32 RADIOGENESIS IN EVOLUTION. 



And it would surely be hypocritical to deny that nature 

 manifests its "" gladiators' shows", even though the ami)hi- 

 theatre be an Eden. 



We have now on record a multitude of examples of a 

 wide range of radial variation in many groups. For the 

 purposes of this paper but two instances are given. In 

 the Hawaiian Islands the song birds which constitute the 

 family Drepanidse show remarkable diversity. Each island 

 has its group of species, and some of these are confined 

 to a small district, '■ to a single kind of thicket, or a single 

 species of tree." To quote Jordan and Kellogg. " In this 

 family are about forty species of birds all much ahke as to 

 general structure, but diverging amazingly from each other 

 in the form of the bill, with, also, striking differences in the 

 colour of the plumage. ... we find Drepanidae in 

 Hawaii fitted to almost every kind of life for which a song 

 bird in the tropics may possibly become adapted."* For 

 the second example we may quote, from the same authorities, 

 the land snails of Oahu. (Hawaii.) " According to Mr. 

 Gulick, the land snails of the wooded portion of Oahu have 

 become split up into 175 species represented by TOO or 800 

 varieties. He frequently finds a genus represented in 

 several successive valleys by aUied species, sometimes 

 feeding on the same and similar plants. In every case, 

 the valleys that are nearest each other furnish the most 

 nearly alHed forms, and a full set of the varieties of each 

 species presents a minute gradation between the more 

 divergent types found in the more widely separated locali- 

 ties."! The establishment of these variations, in both 

 birds and snails, is almost certainly due to isolation, but the 

 actual variabihty itself may be well expressed by a principle 

 of Radiogenesis. 



It is now an axiom that similar structures have been 

 independently developed in different groups. " The eye." 

 says Hans Gadow, "" has been invented dozens of times. "J 

 Walter Stapley writes : "It seems a process of narrow 

 reasoning which admits the origin of new species, but refuses 

 to admit that new structures mav be evolved. The denial 



*■' Evolution and Animal Life," p. 124. 

 tOp. cit.. i>. 123. 

 JOp. cit. 



