SPAWNING BEHAVIOR IN FUNDULUS HETEROCLITUS. 317 



extends nearly at right angles from the belly and is thick and 

 stiff and well adapted for supporting the weight of the two bodies 

 and often becomes much inflamed by frequent contact with the 

 bottom. The male, clasping the female firmly as he does, holds 

 his entire body against hers for from one to two seconds. While 

 in this position a quivering vibration of the posterior half of the 

 bodies of both fish occurs, during which eggs and sperm are 

 extruded in very intimate contact with each other. Whether 

 this vibratory movement is initiated by one or both sexes I can- 

 not say for certain, but I am inclined to believe that the female 

 only is responsible, the male simply remaining passive and taking 

 up the vibration from the female. My reasons for believing that 

 such is the case are : first, the vibratory rhythm of the two fish 

 spawning together is always in perfect unison, which would hardly 

 be the case when two fish of very different sizes clasp ; second, I 

 have often seen females assuming the spawning attitude and going 

 through the vibratory movement when there were no males in 

 the vicinity. 



This spawning act is highly adaptive in several respects : 



1. The vibratory movement serves to extrude ripe eggs and 

 ripe sperm at the same instant. It is only in this way that the 

 sexual products can be extruded as is shown by the fact that the 

 females are forced to adopt this method of relieving themselves 

 when there are no males present. 



2. The position assumed by the two sexes is such that eggs 

 and sperm are extruded in very close proximity and could scarcely 

 fail to come in contact. Chances of failure are minimized by the 

 fact that on the one hand the milt is shot out with considerable 

 force directly at the eggs as they are extruded, and on the other 

 the eggs exert a strong chemotactic influence upon the sperm, 

 which I demonstrated by the following experiment. A freshly 

 stripped egg was put on a glass slide with a few drops of water 

 and then a drop of sperm was put in the water at a distance of 

 half an inch. In a very short time the egg was surrounded by a 

 dense cloud of sperm and inside of two minutes all of the sperm 

 was seen to be gathered about the egg. In addition to this the 

 surface of the egg is very glutinous and probably holds all sperm 

 that comes in contact with it. 



