The albumen or white is not exactly of the same composition in the eggs of different birds ; but it generally contains alhninen with salts and a compound of sulphur in solution. In the yolk of birds' eggs they recognise the principle first distinguished by Dumas and Cahours as ntelline, a substance precipitable by mixture with a large quantity of water, and apparently more nearly resembling fibrine than albumen in its composition and some of its properties. The phosphuretted fat of the yolk is somewhat similar to the cerebral fatty matter.
The glairy white of the eggs of cartilagi nous fishes is very different from that of birds' eggs, being neither soluble in water nor coa gulable by heat nor acids to the same degree. It seems to contain only traces of organic matter. The angular and tabular particles of the yolk of cartilaginous fishes are com posed of a principle which these authors re gard as peculiar, and have named Ichthine. This substance is insoluble in water, alcohol, and ether, and, on being dissolved hy hydro chloric acid, gives no violet colour, as albu men does. It is dissolved by all the concen trated acids, and by dilute acetic and phos phoric acids. Its composition is stated to be as follows : carb. 51 ; hyd..6-7 ; nit. 15; ox. 25.4.; phosph. 1•9.
In the ova of osseous fishes these authors do not find the same organic principle, but have detected two others in variable propor tions. One of these, which they have named Ichthidine, exists only in small quantity, and is absent in some fishes : it is quite soluble in water. The other which is more generally prevalent and in larger though variable quan tity is precipitated by water into a viscous substance. This has been named Ichthuline. Messrs. Valenciennes and Fremy have ascer tained the interesting fact that while these principles, especially ichthuline, exist in large quantity in the ova at an early stage of their growth in the ovary, they gradually diminish in quantity or are changed as the ova ap proach maturity, and give place chiefly to albumen, which holds the phosphuretted fat in suspension. In the salmon's egg there is a large proportion of ichthulinc, which is the cause of their becoming opaque when water enters the yolk. These authors propose in deed this character as a test of the maturity of the ova, as they are not rendered opaque by water Nvhen mature. It would be inte resting to know whether fecundation produces any inunediate chemical change on the prin ciples of the yolk. The composition of ich thuline is stated to be as follows : carb. 52.5 ; hyd. 8 ; nit. 15-2; ox. 22'7 ; phosph. 0'6 ;
sulph. 1.
The ova of Batrachia seem to resemble most nearly those of cartilaginous fishes, in so far that the tabular particles of the yolk are composed of ichthine. The external ge latinous covering is described as a tissue of hyaloid membrane which absorbs water in a determinate quantity-.
The ova of Ophidia and Sauria resemble nearly those of birds in the composition of the white and yolk, containing the principle vitelline in the latter. The yolk of the Viper presents the singular peculiarity of becoming gelatinous by immersion in water.
In the ova of several Chelonia they have detected a different principle from vitelline to which they give the name of vitelline. This principle is soluble in potash, and has the following composition: carb. 49-4 ; hyd.7-4; nit. 15-6 ; ox. and phosph. 26.7.
Among the invertebrate animals Messrs. Valenciennes and Fremy have examined the ova in several classes. In the Crustacea they have given much attention to the in vestigation of the curious colouring principle of the ova, which appears to be the same as that existing in the shell, and which being green in the moist state passes into red in a variety of circumstances. They have isolated this colouring matter by a very simple pro cess, and give an interesting account of its properties, especially of the circumstances causing it to change to red, such as the ac. tion of alcohol, boiling, desiccation, placing in a vacuum, friction, &c.
The ova of Arachnida and Insects are quite different from those of Crustacea in their composition, containing albumen, fatty matters, and a large quantity of a substance precipitable by water.
The ova of Mollusca differ greatly in com position from those of other animals : more particularly in the entire absence of fat from them.
From these researches it appears that there are considerable differences in the chemical composition of the ova of animals of different great groups, and even among those not far removed from each other in the zoological scale, and that there are also considerable differences according to the state of advance ment of the ova of the same animal, more especially it would appear that a marked change of composition takes place at the period of complete maturity. The researches referred to appear to have brought to light several new organic principles which are modifications of albumen or belong to the same class, and which may be considered as Vitelline principles as belonging to the yolk of different animals : such are Vitelline, Ich thine, Ichthidine, Ichthuline, and Emydine.