Page:Popular Science Monthly Volume 56.djvu/496

482 of one hundred and eight in a small specimen. Dr. Loeb has called my attention to the more rapid absorption of oxygen in the light than in the dark; this extended would probably mean the more rapid absorption of oxygen through the skin of light-colored animals, a matter of doubtful value, however, to species living in the dark.

The gill filaments are small as compared with the gill cavity. Oxygenation probably takes place through the skin. Ritter has suggested the same for Typhlogobius.

"Cutaneous respiration is not unique in Typhlogobius and the Amblyopsidæ. In the viviparous fishes of California the general surface, and especially the fins, which have become enormously enlarged, serve as respiratory organs during the middle and later periods of gestation; the fins are a mass of blood-vessels, with merely sufficient cellular substance to knit them together. There is, however, no pink coloration."

Skin respiration would account for the extreme resistance to asphyxiation in Amblyopsis and Typhlogobius. About forty-five examples of Amblyopsis were carried in a pail of water four hundred miles by rail, with only a partial change of water three times during twenty-four hours. A smaller number may be kept for days or weeks—probably indefinitely—in a pail of water without change. The characteristics of Typhlogobius along this line have been set forth elsewhere.

Sticks, straws, etc., are never avoided by the fishes even when perfectly imperturbed. By this I mean that they are never seen to avoid such an object when it is in their path. They swim against it and then turn. An object falling through the water does not disturb them, even if it falls on them. A pencil gently moved about in front of them does not disturb the fishes much, but if the pencil is held firmly in the hand it is always perceived, and the fish comes to a dead halt ten or fifteen millimetres before it reaches such an object. On the other hand, they may be touched on the back or tail before they start away. They glide by each other leisurely and dignified, and if they collide, as they sometimes do, they usually show no more emotion than when they run against a stick. But this indifference is not always displayed, as we shall see under the head of breeding habits.