30 EVOLUTION AND DISEASE. 4 
two halves of the mantle, penetrated between the mantle 
and the shell. The irritation thus caused induced the 
mollusc to cover the intruder with pearl. The secretion — 
must have taken place in a very short time, at any rate 
before the fish could have been destroyed by decom. _ 
position, 
Fic. 16.—A fish embedded in pear! (after Giinther). 
Dr. H. Woodward has described some interesting : 
specimens of the same nature. He exhibited before the © 
Zoological Society (1886) a Pzxnotheres which had been ; 
entombed in a cyst of pearl by a pearl-mussel. In connec- — 
tion with the specimen Dr. Woodward made the following | 
j 
