486 POPULAR SCIENCE MONTHLY. 



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 punch- 

 ing is of a different order. While jerking through the water im- 

 mediately 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 aqua- 

 rium, 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 male- 

 ness 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, sa'prolegnia, 

 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 de- 

 stroyed 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 greed- 

 ily devoured. Fish mold is the bane of the larvae. Many of them 

 were found with tufts of the hyphen growing out of their mouths 

 and gill openings. 



* Since the above was written an apparently successful atten-pt has been made to col- 

 onize them in a pool at Winona Lake. A record of this colony will be published later. 



