COMPLETE SEX-REVERSAL IN VIVIPAROUS TELEOST. 99 



had given birth to forty young on the second of June and fifty- 

 three on the fourth of May failed to bring forth young. It is 

 necessary to state here that the species under consideration 

 reproduces monthly with almost chronological regularity. At 

 the time mentioned there were no definite signs of sex-reversal 

 and it was thought that owing to some change in environment, 

 birth of young was delayed. A month later, that is the beginning 

 of August, signs were available as to what was going on with 

 female Bi6. September the I2th, when the writer left for 

 Norman, Oklahoma, to occupy his present position, the fish had 

 reached advanced stages of sex-reversal. 



Owing to the courtesy of Dr. G. W. Tannreuther of the 

 Department of Zoology, to whom I wish to express my indebted- 

 ness, my research material reached Norman in good shape a few 

 weeks later. Female Bi6 was an unmistakable male except 

 body form by the first of December and was mated to a virgin 

 female. On February 25, 1924, this pair gave birth to eight 

 young, all of which were to all appearances normal. Two weeks 

 later five of the young fish died owing to a sudden drop of 

 temperature. The remaining three reached sexual maturity 

 with one male and two females as a sex-ratio. 



The stock was greatly increased in the spring of 1924 when 

 additional material was procured from the Crescent Fish Farm. 

 A larger number than ever before of adult females, not less than 

 three years of age, were isolated for observation. Of this group 

 three females transformed to males before the end of the year. 

 One, female 032, transformed without previously giving birth 

 to young and for this reason is dismissed from further considera- 

 tion in this study. Female C3 gave birth to one litter and 

 female 14 three litters of young before sex-reversal took place. 

 Both fishes were mated to virgin females, but young were 

 obtained only from the mating in which 3 was the male. 

 From this mating five young were obtained, all of which reached 

 sexual maturity. The sex-ratio was two males to three females. 



As stated above, in the mating in which 14 was the male no 

 young were obtained. The mating was repeated with other 

 virgin females but without success. Upon killing, the autopsy 

 revealed malformation of the sperm duct which was obstructed 



