Licence: Public Domain Mark
Credit: Ovum / by Allen Thomson. Source: Wellcome Collection.
Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.
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![the yolh ; and BischofF states that they gra- dually disappear, or are dissolved without obvious change. We are at a loss to deter- mine what office these globules may have in connection with the changes of the ovum at the time they appear. Lastly, I would notice the interesting re- lation which appears to subsist between the situation of the germinal vesicle and the cen- tre of the germinal membrane afterwards formed, or the germinal pole of the ovum, and the conformity in the direction of the line of the first cleavage of the yolk with that of the principal axis of the embryo in verte- brate animals. The first fact has been observed in all animals, and the latter has been ascer- tained by Mr. Newport’s researches in Ba- trachia, and by observations which I have myself made in the bird’s egg during its de- scent through the oviduct. These facts, as yet inscrutable in their nature, point to in- teresting laws relating to the connection of the first phenomena of development, which may be worked out by the further prosecution of these inquiries. In the preceding part of this article we have considered chiefly the anatomical struc- ture of the ova of animals, and have made little mention of their chemical composition. The knowledge of the latter subject is as yet very imperfect. In a recent Memoir* Messrs. Valenciennes and Fremy have given an ac- count of an extended series of experimental researches in which they have been engaged, with a view to determine the differences in the chemical composition of the ova of dif- ferent animals, and although this investigation is still necessarily incomplete and fragmentary, they appear already to have arrived at some interesting results. The following are some of the more important of these results. The albumen or white is not exactly of the same composition in the eggs of different birds ; but it generally contains albumen with salts and a com()Ound of sulphur in solution. In the yolk of birds’ eggs they recognise the principle first distinguished by Dumas and Cahours as Vitelline^ 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 by hydro- chloric acid, gives no violet colour, as albu- men does. It is dissolved by all the concen- * See Journal de Pharmacle, &c., vol. xxv. pp. 321. and 415., and vol. xxvi. p. 5., 1854. [14^1] 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 ichthuline, which is the cause ot 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 when mature. It would be inte- resting to know whether fecundation produces any immediate 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](https://iiif.wellcomecollection.org/image/b24918751_0147.jp2/full/800%2C/0/default.jpg)
