Page:Proceedings of the Royal Society of London Vol 1.djvu/395

Rh The eggs, however, are not loose as in the oviducts of birds, but are grouped together to the number of three, four, or ﬁve, in membra- nous bags, containing a transparent jelly, in which the young ﬁsh swims about after it is formed, with the yolk attached to its belly by a long chord, consisting of blood—vessels. If the bag be torn and the ﬁsh taken out and put into water with its yolk attached to it, it swims about; but if the vessels of the chord are wounded, it dies im- mediately.

The author is of opinion that many of the shark tribe have this mode of hatching; but with respect to the large shark between the tropics, the fact has been already observed by Dr. Patrick Russell, who in one instance found twenty-one young ones in the right oviduct, and twenty in the left.

The gelatinous liquor surrounding the ova being found to differ in its properties from their animal jellies, excepting that with which the ova of frogs are surrounded, Mr. H. procured some frogs that he might watch the formation of their jelly, and examine its properties. No change was observed to take place in their ovaria through the winter, but on the 10th of February when a portion of oviduct was immersed in water at 80°, it swelled to double its size, and even larger when the water was warmer. 0n the 25th of February a portion of oviduct, only two or three inches long, being put into water at 120°, stelled to such a mass of transparent jelly as ﬁlled a half pint tum- bler. This substance resembled what is occasionally found on the ground, and on the branches of trees, and is called star-shot jelly; which by Pennant has been supposed to be brought into that state in the stomachs of herons and of other birds that feed on frogs, and then rejected by vomiting.

Mr. Brande was consequently requmted to make a comparative examination of the jelly from the shark, of the jelly obtained from the oviducts of frogs, and of star-shot jelly, procured from Lincoln- shire; and he found them to agree perfectly in their properties.

When dried they become brittle, but when put into water, they expand again to their original bulk, even although the heat of boiling water has been applied for drying them. Water does not appear to dissolve any portion of them even by boiling; they dissolve, however, by acids or by alkalies. As none of the solutions are precipitated by tannin, the substance distinctly differs from gelatin; and as it is not coagulated by heat, by acids, by alcohol, or by electricity, it differs equally from albumen, and must be considered as of a peculiar nature not yet described.

The subsequent part of Mr. Home’s communication relates to the provisions for supplying the foetus of different animals with air.

The ova of many ﬁsh are laid as near the sources of rivers as they can be, for the sake of the greater proportion of air contained in the water. Others are attached to plants which assist in supplying them with oxygen. The ova of sharks and of skates, which have their coats too strong to be penetrated by sea-water, have apertures at each end for its admission and escape.