XII. D,s Scale: The Mosquito Fish 179 



BIRTH OF THE YOUNG FISH 



. The mosquito fish does not lay eggs, but gives birth to fully 

 formed and very active young. The exact procedure of each 

 parent in this important function is given below, being described 

 from observations of the actions of a half-grown female mos- 

 quito fish, length, 34 millimeters, and of a young male, length, 

 23 millimeters, which were placed in a small glass jar on my 

 study table where they could be observed perfectly. Obser- 

 vations began December 8, 1915. 



As soon as the male saw the female, he became greatly 

 excited, as was indicated in the swift change of color to a 

 beautiful opalescent blue on the head and the sides. He at 

 once made swift dashes at the female, and acted as if he intended 

 to bite her on the lower abdomen. He made no attempt to 

 copulate with her. The female strongly resented these actions 

 and tried to escape. The male continued the swift dashes and 

 attacks upon the female for ten minutes. The female finally 

 became quiet near the bottom of the jar and gave birth 

 instantly to a young fish, which came out head first and shot 

 to the surface of the water, where it swam about vigorously. 



The male fish in the meantime had become perfectly quiet, 

 resting about 2 centimeters directly behind the female. His 

 great interest and excitement, however, were well shown in the 

 rapid working of his gills, the quick vibration of his caudal fin, 

 and the beautiful play of iridescent blue over his body. 



As soon as the young fish was born the female swam away, 

 but she was again vigorously and continuously attacked by the 

 male until she again became quiet and gave birth to another fish. 

 This one appeared tail first and was delivered with great dif- 

 ficulty. The operation lasted eight minutes. During this time 

 the female left her position repeatedly, but each time was driven 

 back by the male, who exhibited the most intense excitement, 

 except when the female became quiet and attended strictly to her 

 business, at which time he also became quiet and refrained from 

 any attack upon her. 



This female gave birth to 21 young fish, all but 2 coming into 

 the world head first, which may be assumed as their normal 

 manner of birth. The time consumed in the entire operation 

 was twenty-five minutes. 



Within one hour after the young were born, the mother made 

 a fierce attack upon her offspring and succeeded in catching 

 and eating two. These were hard to catch, and I believe that in 



