550 



Prof. M'lntosh's Notes from the 



15 had no pearls and 16 had one or more^ so that nearly 

 50 per cent, in this instance had pearls of a kind^ for 

 they were of no value. Of these, 8 contained only one 

 pearl, four had two, two had four of different sizes. 

 These, hoAvever, came from a well-known curve of the Tay 

 ■which has always been rich in pearls, and where otters and 

 ducks abound. Dr. Lyster Jameson is of opinion that 

 otters^ for instance, might be the final hosts, as, like the 

 raccoon, mink, and musk-rat of North America, it is stated 

 they occasionally eat mussels. The next collection of mus- 

 sels, which exceeded the former in number, did not contain 

 one pearl. In former years, when hundreds were examined 

 on the banks of the Tay at Murthly, the same irregularity 

 prevailed, many having none^ whilst others contained one 

 or more. 



In order to test the frequency of their occurrence in the 

 common mussel of the estuary of the Eden, Mr. Russell 

 examined 700 for me. Of this number 620 were large 

 mussels and 80 small — some very small. Of the 650 

 large mussels, pearls were found in 280 — that is to say, 

 340 had no pearls ; and of the 80 small mussels, 20 had 

 pearls and 60 were devoid of them. In dealing Avitli the 

 pearl-bearing forms, both large and small, and which thus 

 number 800, the following table gives the precise number of 

 pearls in each series, as well as the totals : — 



The proportion of the 300 pearl-bearing mussels to the 

 total number (700) is thus 42'8 per cent. ; but if the large 

 mussels alone are considered, the proportion is higher, 

 viz. 45"1 per cent., which indicates that the common mussel 

 more or less follows the same law as the pearl-oyster, viz., 

 that the older forms produce most pearls. Indeed, the 

 number of pearls in the very small mussels at St. Andrews 

 is noteworthy, and may be explained by the fact that the 

 very small are not necessarily young mussels, as a glance 

 at the crowded masses of minute forms on the rocks show. 



