MONSTROSITIES. 
103 
development of spiral or radiate dull white lines, make it desirable 
that these peculiarities should be treated of under this head. 
Fig. 216 . — Anodonta cygnca (L. ), 
Sandwill Park, Staffordshire, collected by Mr. J. Madison, 
Showing the effects of some severe laceration of the mantle, the result of which is seen in the 
strongly separated parts of the left valve and in the deeply-furrowed right valve. 
Monstrosities. 
Monstrosities are generally considered to he those individuals 
whose differences arise from pathological causes ; the name is like- 
wise very aiipropriately applied to those malformations which may 
be congenital and transmissible from one generation to another, as is 
sometimes the case with the reversed monstrosities, although 
M. Sanier, who endeavoured to perpetuate the reversed form of Ileliv 
aspersa by accumulating several adult specimens and breeding from 
them, found the few resultant progeny all dextral, and this experience 
has been confirmed by others. The term monstrosity also indicates 
specimens which have become deformed during growth, owing to some 
intrinsic or extrinsic irritation or disturbance, perhaps causing 
