Omphalos: An Attempt to Untie the Geological Knot

by Philip Henry Gosse

This very peculiar protecting capsule points clearly to a peculiar structure in the parent. The embryo was not inclosed in the pillow-case, at its first formation; but, in the course of its descent from the ovary through the oviduct, it had to pass a region of the latter, where was a thick glandular mass,—the nidamental gland,—whose office it was to secrete a dense layer of albumen, with which, the embryo became invested. This substance took the form of the flattened purse, or pillow-case, with produced angles, above described, and on its exclusion from the duct assumed a very tough horny consistence, and a dark mahogany colour.

The comparative anatomist would, therefore, without the least hesitation, refer the origin of the investing capsule to the nidamental glands of the female Shark; but supposing the embryo to be but just created, his physiological science would only lead him to a false conclusion.

If the Tree-frog afforded us evidence of pre-existent time, in the metamorphosis which it must naturally have experienced from the tadpole to the reptilian condition, what shall we say to that strange and uncouth member of the same class,—the Surinam Toad (Pipa)? Little would be gained by selecting the germ-stage, as the presumed epoch of creation in this case; for, according to the extraordinary economy of this genus, the male acts as midwife, and the female as wet-nurse, to the hopeful progeny.

"As fast as the female deposits her eggs, the male who attends her arranges them on her broad back, to the number of fifty or upwards. The contact of these eggs with the skin appears to produce a sort of inflammation; the skin of the back swells, and becomes covered with pits or cells, which enclose each a single egg, the surface of the back resembling the closed cells of a honeycomb. The female now betakes herself to the water; and in these cells the eggs are not only hatched, but the tadpoles undergo their metamorphosis, emerging in a perfect condition, though very small, after a lapse of eighty-two days from the time in which the eggs were placed in their respective pits."

To a tyro in animal physiology it might seem that the smooth rounded egg of a bird or a lizard, presents an example of an organism in the simplest possible condition, and in a stage which, if any can be, is independent of anything that went before.

But is it so? Let us see. Here is the egg of the common Fowl. I take it in my hand, and perceive nothing but an uniform, smooth, hard, white surface. This I break, and find that it is a thin layer of calcareous substance, which, on microscopical examination, proves to be composed of minute polygonal particles, so agglutinated as to leave open spaces in the interstices of their contiguous angles.

Below this calcareous shell I find a membrane (membrana putaminis), which seems, from its thinness in most parts, to be single, but which is separated into two layers at the large end of the egg.

HEN'S EGG.

Within this membrane there is another (the chalaza) which, closely enveloping the yelk, passes off from it towards each extremity of the egg in the form of a twisted cord.