30 E VOL UTION AND DISEASE. 



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. 



FIG. 16. A fish embedded in pearl (after Giinther). 



Dr. H. Woodward has described some interesting 

 specimens of the same nature. He exhibited before the 

 Zoological Society (1886) a Pinnotheres which had been 

 entombed in a cyst of pearl by a pearl-mussel. In connec- 

 tion with the specimen Dr. Woodward made the following 



