SEX-RATIOS IX GAMBUSIA HOLBROOKI. 183 



The testes vary in size with the season and the individual. 

 Thus, the median length of 19 taken at random on July 20, 1920 

 was 3.2 mm. and the median breadth 2.2 mm.; while the median 

 length of five taken November 23, 1920 was 2.75 mm. and the 

 median breadth 2.07 mm., a volume relation of approximately 

 1.6 to i. The testes in individuals of the same litters vary but 

 little in size, but they vary greatly in individuals of the same 

 size taken from different litters. 



TEXT-FIGURE i. Lateral dissection of a male Gambusia holbrooki showing 

 the general relations of gonopod to other organs, especially the internal organs 

 of the body. /, intestine; T, testis ; AF, gonopod ; HS, modified haemal 

 spines ; M, muscle controlling gonopod ; VP , ventral process of abdominal 

 vertebrae. (After Kuntz, '14.) 



There is no prominent connective-tissue core in the testis of 

 Gambusia such as Turner ('19) described for the perch, and 

 Brock ('78, Taf. xxviii, Fig. 3) figured for Perca fluviatilis. 

 The testes of Gambusia consist of a tenuous, diffuse, connective 

 tissue stroma, in the interstices of which the spermatogonia and 

 cysts are closely packed. The structure of the adult testis re- 

 sembles very closely in some respects that observed by von 

 Ihering ('83, p. 486) in the South American pceciliid, Phallo- 

 cerps caudomaculatus. The smaller cysts of multiplying sper- 

 matogonia lie in the cortical portion of the testis. As one pro- 

 ceeds inward the cysts become more and more mature. The 

 cysts in the spermatid stage are much larger than the mature 

 sperm-balls, or spermatozeugmata. The latter lie closest to 

 the center of the testis, and near to (and with) the longitudinal 

 canal, which appears to serve as a storage place for sperm ; the 

 former, more peripherad. After the growth-period preceding 

 the I.-spermatocyte division, the cysts are much larger than 



