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Updated: May 9, 2025
Our lungs, trachea, and larynx are formed from the ventral wall of the branchial gut. These vesicles are found in all the Vertebrates except the two lowest classes, the Acrania and Cyclostomes. In the lower Vertebrates they do not develop into lungs, but into a large air-filled bladder, which occupies a good deal of the body-cavity and has a quite different purport.
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 branchiæ.
The abdomen ends in three long and many jointed stylets, and there are the usual "false branchial feet" along each side of the abdomen. There are two European species which occur in greenhouses. No species have yet been found in America. The next family of Thysanura is the Campodeæ, comprising the two genera Campodea and Japyx.
It is a question of nothing less than of transforming him into furnished lodgings. The female fish bears underneath her tail a prolongation of the oviduct; she introduces it delicately between the Mollusc's valves and allows an egg to fall between his branchial folds. In his turn the male approaches, shakes himself over it, and fertilises it.
It is also called the branchial cavity and the cloaca, because it receives the excrements and sexual products as well as the respiratory water. This is so like the gill-crate of the Amphioxus in its whole arrangement that the resemblance was pointed out by the English naturalist Goodsir, years ago, before anything was known of the relationship of the two animals.
This latter movement is effected solely by the aid of the pectoral fins; the tail being collapsed, and not used. From the body being buoyed up with so much air, the branchial openings are out of water, but a stream drawn in by the mouth constantly flows through them.
In these important Vermalia the foremost section of the gut has already been converted into a gill-crate, and the vascular arches that rise in the wall of this from the ventral to the dorsal vessel have become branchial vessels. We have a further important advance in the Tunicates, which we have recognised as the nearest blood-relatives of our early vertebrate ancestors.
The jaws are modified branchial arches or the cartilaginous or bony rods which in our present fish support the fringe of gills. These have formed a pair of exceedingly effective and powerful jaws. The reproductive system holds still to the old type and shows little if any improvement.
But the EXTERNAL, superficial branchial skeleton that supports the gill-crate in the Cyclostoma is replaced in the Gnathostomes by an INTERNAL branchial skeleton. It consists of a number of successive cartilaginous arches, which lie in the wall of the gullet between the gill-clefts, and run round the gullet from both sides.
We cannot, for instance, suppose that in the embryos of the vertebrata the peculiar loop-like courses 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.
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