184 S. W. GEISER. 



before, von Ihering's description of the formation of a sper- 

 matozeugma in Phalloccros holds also for Gambusia. 



The testis of Gambusia lacks the tubular type of structure 

 characteristic of the testes of oviparous Pceciliids, e.g. Fundulus. 

 Apparently there has come with viviparity in this family fertili- 

 zation of the eggs of the female by means of sperm-balls, which 

 appear to be formed in the same way in all viviparous members 

 of the family Pcecttiidce examined. 



-i 



peripheral layer 

 of early stages 

 _ J^>> Y-^ "X 







^m 



-band of early stages 



(central portion 

 Of early 3p.-zeugnata 

 cysts) 



peripheral layer of cyst 

 In early stages. 



TEXT-FIGURE 2. A portion of the testis of Gambusia, showing the differ- 

 ential development of spermatocytes indicative of the original paired condition 

 of the testis. 



In the adults the two testes are very closely fused ; the double 

 structure being evidenced only by the almost universal separa- 

 tion of the longitudinal testicular canal into two portions, one 

 ramus on either side of the median line in the anterior four- 

 fifths of the testis ; and in the differential development of sper- 

 matocytes (Text-fig. 2). 



In the testis figured the major portion of the gonad consisted 

 of cysts in spermatid and early spermatozeugma-stages. These 

 occupied the central portion of the testis, grouped about the 

 paired longitudinal testicular canals. At the periphery there 

 were cysts whose cells were in early I.-spermatocyte division 



