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Updated: May 9, 2025
We may cease marvelling at the embryo of an air-breathing mammal or bird having branchial slits and arteries running in loops, like those in a fish which has to breathe the air dissolved in water, by the aid of well-developed branchiae.
We cannot, for instance, suppose that in the embryos of the vertebrata the peculiar loop-like course of the arteries near the branchial slits are related to similar conditions, in the young mammal which is nourished in the womb of its mother, in the egg of the bird which is hatched in a nest, and in the spawn of a frog under water.
Dichelaspis Darwinii was found by Filippi in the branchial cavity of Palinurus vulgaris, and I have met with another species of the same genus in the branchial cavity of Lupea diacantha. The same thing may have taken place in primitive times.
All the interesting features of these skulls that clearly indicated the transition from the anthropoid to the man were declared by Virchow to be chance pathological variations. We turn now to the branchial arches, which were regarded even by the earlier natural philosophers as "head-ribs."
On the other hand, the alimentary canal becomes a most extensive organ. It divides presently into two sections a wide fore or branchial gut that serves for respiration, and a narrower hind or hepatic gut that accomplishes digestion.
These pass with the water into the gill-crate and the digestive part of the gut at the end of it, at first into an enlargement of it that represents the stomach. The outlet is sometimes called the branchial pore, and sometimes the cloaca or ejection-aperture. In many of the Ascidiae a glandular mass opens into the gut, and this represents the liver.
Thus when a wave of water escapes from the branchial cavity, it immediately becomes diffused in this network of hairs and then again conveyed back to the branchial cavity by vigorous movements of the appendage of the outer maxilliped which works in the entrant fissure.
Somehow or other, the eggs of the female are conveyed into the mouth of the male, the bottom of which is lined by them, between the inner appendages of the branchial arches, and especially into a pouch formed by the upper pharyngeals, which they completely fill.
After having been taken out of water for a short time, and then again immersed in it, a considerable quantity both of water and air is absorbed by the mouth, and perhaps likewise by the branchial orifices.
Whilst the hinder part of the carapace rises and the above-mentioned fissure is formed, the anterior part seems to sink, and to narrow or entirely close the anterior entrant orifice. Under water the elevation of the carapace never takes place. The animal therefore opens its branchial cavity in front or behind, according as it has to breathe water or air.
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