394 Proceedings of the Royal Physical Society. 



Wednesday, 25th April 1866. — Professor John Duns in the Chair. 



The following Donations to the Library were laid on the Table, and 

 thanks voted to the Donors : — 



1. Geological and Natural History Repertory, Nos. 10,11, 12, with 

 Proceedings of Geologists' Association. 1866. — From the Geologists, 

 Association. 2. The Canadian Journal. No. LXI., January 1866 — 

 From the Canadian Institute, Toronto. 3. Observations on arrested 

 Twin Development. 1866. By P. D. Handy side, M.D.— From the 

 Author. 



The following Communications were read : — 



I. The Pearls of the Ythan, Aberdeenshire. By the Rev. James Brodie, 

 Monimail, Fife. 



These mussels are, of course, of various sizes, and are found 

 sometimes in the running stream, and sometimes in the 

 pool. I found them most abundant in those places where 

 the bottom consisted of a softish sand, with a gentle current 

 flowing over it. The pearls are embedded in a filmy sub- 

 stance that occupies the space between the valves and the 

 body of the animal. There is not a pearl, even of the 

 smallest size, in every mussel ; on the contrary, I have fre- 

 quently gathered more than a hundred and have not found 

 anything whatever to recompense my trouble. 



I remarked that, generally speaking, the shells collected 

 in the streams, where they had been exposed to the tossing 

 of the winter floods, most abundantly rewarded the gatherer's 

 toil, and that those which were distorted and bore the marks 

 of having been broken by violence, were those in which 

 pearls were most frequently found. These circumstances 

 led me to conclude, that the pearl is produced by some piece 

 of broken shell or extraneous matter getting embedded in 

 the filmy substance to which I have just referred, and by 

 the irritation which its presence produces inducing around 

 it a deposit of the same substance as that which lines the 

 shell. I was led to regard the formation of the pearl as 

 the result of an accident rather than as the effort of a disease, 



as many have supposed The patronage of the 



Queen has made the Scottish pearl to be so much more 



