XII, D, 3 



Seals : The Mosquito Fish 



181 



On April 6, 1916, forty-three days after the last spawning, 

 this female gave birth to 49 young. 



During this spawning the male fish was removed to another 

 jar. The young fish were born without difficulty and in record 

 time. Therefore, while it might seem that the presence of the 

 male was essential to the spawning, it is evidently not so. This 

 female was kept under close observation for six months, during 

 which time she gave birth to six broods of young as follows : 



Table I. — Number of young and dates of six broods of mosquito fish. 

 Total, 233 fish in less than six months. 



Brood. 



Young. 



Date of birth. 



First 



21 

 48 

 49 

 36 

 40 

 39 



Dec. 8, 1915. 

 Feb. 26, 1916. 

 Apr. 6, 1916. 

 Apr. 27, 1916. 

 May 30, 1916. 

 June 23, 1916. 





Third 



Fourth -- 



Fifth 



Sixth - - 



Total .... 



233 







EMBRYOLOGY 



The embryology and morphology of the reproductive organs 

 of the mosquito fish have been worked out by Kuntz," and a brief 

 summary of his paper follows. 



The ovary of Gambusia affinis is a paired tubular organ without a distinct 

 median wall, which opens directly into the urogenital sinus. Each ovum is 

 contained in a separate cellular follicle in which fertilization takes place 

 and the embryo is developed. At the completion of development the ovarian 

 follicles, which are attached to the central rachis by a slender stalk, are 

 ruptured and the young fish are extruded directly through the urogenital 

 aperture. 



The modified anal fin of the male, which functions as an intromittent 

 organ, is controlled by a powerful muscle, which is inserted on the proximal 

 end of the anal fin rays and has its origin on a bony process projecting 

 ventrally from the fourth to the last abdominal vertebra, and the modified 

 hasmal spines of the first three caudal vertebrae. The third, fourth, and 

 fifth rays of the anal fin are enlarged, greatly elongated, curved, and bear 

 short spines on the distal portion. The interhsemal, which articulates with 

 the third ray, is enlarged and joins with the two anterior processes on which 

 the muscles controlling the anal fin has its origin. 



The testis, like the ovary, is a paired tubular organ. The spermatozoa 

 are contained in the spermatophores and are probably transmitted from the 

 male to the female in these bodies. 



The formation of the blastoderm and the differentiation of the embryo 

 take place in the manner that is quite typical for all the bony fishes. 



"Kuntz, Albert, Bull. U. S. Bur. Fisheries (1913), 33, 181-189. 



