Page:Popular Science Monthly Volume 56.djvu/500

486 the water from side to side, apparently hunting for each other. At this time they are very agile, and move with precision. When the belligerents meet one above the other, the snapping and punching is of a different order. While jerking through the water immediately after a round, if one of the belligerents touches one of the neutrals in the aquarium it frequently gives it a punch, but does not follow it up, and the unoffending fellow makes haste to get out of the road, the smaller ones doing so most quickly. If, after an interval of a few seconds, a belligerent meets a neutral they quietly pass each other without paying any further attention, whereas if the two belligerents meet again there is an immediate response. Whether they recognize each other by touch or by their mutual excitability I do not know. At one time, in another aquarium, I saw one belligerent capture the other by the pectorals. After holding on for a short time it let go, and all differences were forgotten. The thrust is delivered by a single vigorous flip of the tail and caudal to one side. These fights were frequently noticed, and always occurred between males.

The absence of secondary sexual differences in the cave fishes is a forcible argument in favor of sexual selection as the factor producing high coloration in the males. The absence of secondary sexual differences in cave animals opposes the idea of Geddes and Thompson that the differences are the external expression of maleness and femaleness.

Attempts at acclimating Amblyopsis in outside waters have so far failed. A few were placed in Turkey Lake, Indiana. They were surrounded by a fine wire net, to keep off other fishes. They died in a few days, as the result of attacks of leeches, saprolegnia, or fish mold, and from unknown causes. Others were kept in an elongated box sunk into the ground, where fresh spring water flowed through it constantly. Saprolegnia sooner or later destroyed all of them. They live longest in quiet aquaria, where the water is rarely changed. The young I have secured died, with one exception, within a few weeks. The difficulty of rearing the young is not at all insurmountable. They eat readily. Their aquaria must be kept free from green plants, and have a layer of fine mud, with a few decaying leaves, in the bottom. They will feed on minute crustaceans and other micro-organisms. When they have reached a sufficient size, examples of Asellus are greedily devoured. Fish mold is the bane of the larvæ. Many of them were found with tufts of the hyphæ growing out of their mouths and gill openings.