ATAVISM OR REVERSION. 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 (Palznurus 
pentcillatus). 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 antenne, 
eye-stalks, swimmerets, chela, and the like, morpho- 
