200 Sir David Brewster on the Aatomical and Optical 
Plover. Cock. Adjutant. 
Common Pigeon. Hen. Peacock. 
Wood Pigeon. Green Linnet. Kite. 
Emberiza. [ Ornithorhynchus.] Raven. 
Alauda arvensis. Red-tailed Hawk. Gray Parrot. 
Tringa. Trumpeter. Nicobar Pigeon. 
Black Grous. Vulture, Indian. Crested Curassow. 
Red Grous. Cireaetes brachy- Mandarine Duck. 
Partridge. dactylus. Chukar Partridge. 
Wild Duck. Crested Guan. Owl, Indian. 
Pheasant. Condor. [ Macacus Cynomol- 
Penguin. Rhea Ostrich. gus*. | 
Lizarps. 
Lacerta striata. Lacerta Calotes. 
For many of the lenses in the preceding table, and for 
others which I shall have occasion to enumerate in subsequent 
communications, I have been indebted to the kindness and 
zeal of Captain Basil Hall, Captain Robertson, Professor Grant, 
Mr. George Swinton, Dr. Knox, Mr. William Clark, and 
Mrs. Green of Cumberland Island. 
In the Philosophical Transactions for 1816, I have de- 
scribed and represented by drawings the singular structure 
of the crystalline lens of the cod, as exhibited by transmitting 
through it a beam of polarized light. I have there shown that 
it consists of three different structures; viz. the nucleus, which 
has negative double refraction like calcareous spar; the ex- 
ternal strata, which have the same kind of double refraction ; 
and the intermediate strata, which have positive double re- 
fraction like zircon. The axis of vision, or that of the sphe- 
roidal lens, is the axis of double refraction for these three 
structures. I have discovered the same structure in the lens 
of the haddock, the salmon, the frog-fish, the skate, and the 
whiting, and indeed, with more or less distinctness, in all the 
lenses of fishes which were large enough to show the polarized 
tints. 
A doubly refracting structure, related to the axis of vision, 
is distinctly seen in the human lens, and in that of quadrupeds 
and birds; but it differs considerably, both in its character 
and intensity, from that which exists in the lenses of fishes. 
In the paper to which I have already referredt, I have stated 
* For the lenses cf most of these birds, &c. and many others which will 
be described in subsequent papers, I have been indebted to the liberality 
of the Zoological Society. 
+ Philosophical Transactions 1816, p: 315. 
