236 PROCEEDINGS OF SOCIETIES, 
As it appears, therefore, that these crystals consist of carbonate 
of lime, the question remains, What is it that protects themfrom . 
the action of acids ? 
Some light is thrown on this question by the following observa- 
tions : 
Alcohol and ether, even when heated, had ‘not the power of 
removing the protecting substance; but if, after digesting with 
ether, the spicula were boiled in solution of caustic soda and sub- 
sequently immersed in dilute hydrochloric acid, the crystals 
disappeared, and their places were occupied by amorphous patches. 
There is one’ objection that may perhaps be taken to the view 
here adopted as to the nature of the crystals, which may as well 
be noticed. It may be thougut that in the plant the lime was | 
united to some organic acid, say the oxalic. But it will be 
admitted that, putting aside the agreement in form with carbonate 
of lime, the fact of the crystals being unaltered in form by burn- 
ing, and retaining the power of acting on polarized light, is fatal 
to such an hypothesis.—Jouwrnal of Linn. Soc., Vol. VII, p. 106. 
Royat Sociery. 
“ A Contribution to the Minute Anatomy of the Retina of 
Ampuisia and Reprites. By J. W. Hurxe, F.R.CS. 
Assistant-Surgeon to the Middlesex and the Royal London 
Ophthalmic Hospitals. Communicated by W. Bowman, Esq 
Received February 4, 1864. 
(Abstract.) 
The animals of which the retina was examined were the frog, 
the black and yellow salamander, the edible turtle, the water- and 
the land-tortoise, the Spanish Gecko, the blindworm, and the 
common snake. The method adopted was to examine the retina 
(where possible) immediately after decapitation of the animal, 
alone and with chemical agents; and to make sections of the 
retina hardened in alcohol or in an aqueous solution of chromic 
acid, staining them with iodine or carmine, and adding glyceriue, 
pure and diluted, to make them transparent. The following is a 
summary of the results of the examination: 
1. The rods and cones consist of two segments, the union of 
which is marked by a bright transverse line. 
2. Each segment consists of a membranous sheath and contents. 
3. The outer segment, or shaft, is a long narrow rectangle (by 
inference, a prism or cylinder). It refracts more highly than the 
_inuer segment. Its contents are structureless, and of an albu- 
minous nature. It is that part which is commonly known as “ the 
vod.’ It is smaller in the cones than in the rods, and in the cones 
narrows slightly outwards. 
4. The outer ends of the shafts rest upon the inner surface of 
