Notes on the Chough or Red-legged Crow, ^c. 143 
of the required form, and placed between the mantle and the shell of a 
nacre-producing mollusc ; when sufficiently coated, it is filled with mastic, 
and a small plate of mother-of-pearl placed at the back. In regard 
to British pearls, the author stated that the first notice of the gem was 
bj Tacitus in his " Life of Agricola ;" and that the pearls were the pro- 
duct of the fresh- water mussel of our rivers (Unio margaritafera) , was 
evident from the description, that thej were "not very orient, but pale 
and wan." To the theory advanced by Arnoldi in 1696, anew by Sir 
Everard Home in 1818, and also by Kellart in 1858, that pearls, or 
rather their nuclei, were due to the sterile ova of the molluscs which pro- 
duced them, the author gave his decided opposition, as, from all the facts 
which he had observed, pearls were entirely due to a secretion from the 
mantle of the animal. To illustrate the structure of pearls, Mr Bryson 
exhibited a large series of sections which he had prepared, and by which 
he showed that by the microscope he could at once determine what shell 
had produced them. He also explained the rationale of the irridescence 
of mother-of-pearl, — a discovery due to Sir David Brewster, who proved 
that it was due to the diifraction of the rays of light, caused by the out- 
cropping edges of the laminas, and in some cases to the minute plication of 
a single lamina. This phenomenon was also shown by Barton's patent 
buttons, where the irridescence was produced by thousands of minute 
lines, so near each other as to require a high magnifying power to resolve 
them. By taking an impression with black was under considerable 
pressure, the author succeeded in obtaining the same irridescence as exhi- 
bited by the button itself. This experiment Sir David Brewster had tried 
with success in 1815, by taking an impression in wax from a mother-of- 
pearl button , and by which he demonstrated the cause of the phenomenon. 
The commercial value of pearls, the author stated, was still as high as in 
the days of Cleopatra. A good Scottisli pearl, with fine lustre, of the size 
of a pea, fetches from L.3 to L.4. The famous wager between Antony 
and Cleopatra gives us an insight into the value of pearls. The two 
pearls which that luxurious queen resolved to dissolve in vinegar, and 
serve up at the costly banquet, were valued at ten million of sesterces, 
about L. 76, 000 sterling. The pearl in the possession of Mr Hope, M.P., 
the largest of modern times, is not worth a fourth of that sum. The 
weight of this pearl is 3 oz. ; it is 4^ inches in circumference, and 2 inches 
in length. Notwithstanding the great value of the pearls, the shells 
of the animals yield now a far more profitable return than the jewels. 
In 1856, the total value of the pearls imported into this country was 
L. 56, 162, whereas the imports of 2102 tons of mother-of-pearl shells were 
valued at L. 76, 544. Mr Bryson suggested that trials should be made to 
produce artificial pearls from the Iridina^ a nacreous shell, having a much 
higher lustre than any hitherto found. It inhabits the Nile and Senegal 
rivers. 
III. Notes from the neighbourhood of Stranraer — on the Chough or Bed- 
legged Crow (Fregilus graculus) ; on the Migration of the Swift 
(Cypselus apus, Flem.) ; and on the Effects of the severe Gale on the 
9th September last. By the Rev. Thomas B. Bell, Leswalt, Wigton- 
shire. Communicated in a letter to Dr J. A. Smith. 
The Rev. T. B. Bell, in his communication, says, — "The chough is 
common all along our rocky shores, building on clitFs and in caves along 
with his mischievous companion the jackdaw, and sometimes in the same 
cave with the rock pigeon. He annoys the farmers by digging up the 
sprouting wheat, and tearing up the roofs of their stacks. He is not by 
half so wary as either the rook or jackdaw, and consequently falls a fre- 
