A TA VISM OR RE VERSION. 139 



Some instances of the reversions of organs and tissues 

 to an original type will now be considered, and it will 

 serve to simplify matters if the question be illustrated 

 by a botanical example of this form of atavism. In 

 1790 Goethe, in his celebrated treatise " On the Metamor- 

 phosis of Plants," drew the attention of botanists to the 

 fact that the various parts of a flower may be regarded 

 as modified leaves. Of course this does not mean that 

 each part of the flower is a metamorphosed leaf, but that 

 we are able to trace every structural gradation from 

 leaves to bracts, from bracts to sepals, and not infre- 

 quently sepals will be replaced by, or become converted 

 into, true leaves. The changes from sepals to petals and 

 from petals to stamens are as gradual as from bracts to 

 sepals, and the homology is often declared by the 

 stamens becoming petals, and petals appearing as leaves, 

 even stamens have been known to revert in this way ; 

 this is what is meant when we say that the various parts 

 of a flower are formed upon a common type. 



Atavistic phenomena of this character are not un- 

 known in the animal world, some of which we will now 

 consider. 



One of the most remarkable recorded examples of 

 this form of atavism occurred in a rock-lobster (Palinurus 

 penicillatus). It is the specimen originally described by 

 M. Alphonse Milne-Edwards, and referred to by Darwin ; 

 the drawing has been published by Professor G. B. 

 Howes (fig. 77). 



Notwithstanding the differences observed in the 

 various appendages of lobsters, such as the antennae, 

 eye-stalks, swimmerets, chelae, and the like, morpho- 



