102 



THE AMERICAN NATURALIST 



[Vol. XLIV 



normal. Is the reduced number of tarsal joints in the 

 regenerated appendages an indication of reversion to a 

 more primitive condition! No advocate of the atavism 

 theory would be likely to go so far as to oppose the au- 

 thoritative opinion of entomologists which assumes the 

 five- jointed condition as the primitive one. Yet even on 

 its full face value this fact of dropping out of joints is in 

 no sense different from the fact of the addition of an 

 extra finger in the regenerating limb of a salamander 

 which is professed to be a reversion. And, to be consist- 

 ent, should we not also suppose on the basis of Herbst's 

 discovery of the regeneration in Crustacea of antennae 

 in place of extirpated eyes that the ancestors of these 

 animals at the dawn of their history had no eyes, and 

 that the antenna is the precursor of the eye? 



One of the most amusing attempts to mould a regen- 

 erated structural peculiarity into the picturesque shape of 

 an ancestral structure of overwhelming antiquity is that 

 of Schimkewitsch, who very sagaciously interprets the 

 regeneration of an amphibian lens in terms of atavism. 

 As already mentioned in a previous section of the paper, 

 the amphibian lens regenerates not from the skin but from 

 tlic iri-, which is a marked departure from the develop- 

 mental process. This fact leads Schimkewitsch to sup- 

 pose that the paired eyes of vertebrates must have primi- 

 tively been similar to the epiphysis of reptiles, com- 

 monly known as the pineal organ or eye. This pineal 

 organ possesses a lens-like structure which is formed by 

 the thickening of the outer wall of the cup. The purely 

 superficial resemblance of the lens regenerating from 

 the iris of the eye and the lens-like thickening of the 

 pineal organ is the starting point of Schimkewitsch 's 

 hypothesis. He says: 



Urspriinglich die paarigen Augen eine ebensolche Linse besassen wie 

 wir sie im unpaarcn Augen dor Hatteria sehen. d. h. hervorgegangen 

 aus der Wand dor Auirenbhisse selbst. 



It is needless to insist that, in the usual fashion, the 

 author of the hypothesis is appealing for proof to a fan- 



