Gill slit

Definition and stakes

William A. Locy,  Biology and Its Makers

“ The heart and the blood-vessels at this stage are also of the fish-like type, but this condition does not last long; the gill-slits, or gill-clefts, fade away within a few days, and the [Pg 362] arteries of the head and the neck undergo great changes long before the chick is hatched. Similar gill-clefts and similar arrangements of blood-vessels appear also very early in the development of the young rabbit, and in the development of all higher life. Except for the theory of descent, such things would remain a lasting enigma. ”
Source: Gutenberg

Svend Fleuron,  Grim: The Story of a Pike

“ Bleak and little roach revel in her roe; and when she has spawned her heart once more grows cold, and she sinks back into the deep water, gloomy and sullen as before.
Grim becomes more and more eager. Her deep-blue pupils, surrounded with a brass-coloured ring, shine like sapphires in an amber setting; the clayey tones along her sides and flanks change to green, and her gill-covers take on a deep orange hue.
Little by little she feels herself attracted by the numerous eager little male pike that incessantly frisk about her, and are already resplendent in their magnificent golden bridal attire.
”
Source: Gutenberg

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