658 



Sex in Parabiotic Twins 



not quite of the size of A. tigriniim. It appears only once as a mate of a 

 parabiotic pair (jef-T^; fig. 7). All other jeffersonian salamanders of the series 

 (table 3) belong to a medium-sized variety, the eggs of which were collected 

 in the vicinity of Iowa City. Few observations on sex development in jej- 



TABLE 1 



Parabiotic Twins, Series mac-T {Ambystoma maculatumxTriturus torosus). 

 F, normal ovaries; f, inhibited ovaries; M, normal testes; m, inhibited testes; i, indifferent gonads. 



The maculatum members are of the semi-differentiated Ozark race except those of pairs 1 2 and 

 16, which are from Massachusetts and Tennessee. 



No. 



I 



1 

 3 

 4 

 5 

 6 



7 

 8 



9 

 II 



12 

 14 



15 

 16 



17 

 19 



20 

 21 

 22 



Sex glands 



M 



M 



F 



M 



F 



F 



M 



F 



F 



M 



f-F 



F 



M 



F 



F 



F 

 M 



Trilurus 



i(f) 



m 



M 



m 



f 



M 



i(f) 



M 



M 



m 



f 



M 



m 



f 



M 



M 



M 



f 



m 



Age, 

 mo. 



5 

 5 

 4 

 5 

 5 



9 



8 



5 



4 



5 

 8 



7 

 7 

 7 

 8 



5 



5 



5 

 8 



Size, mm. 



A. mac. 



34 

 47 



42 

 40 



36 

 46 



40 

 41 



39 



23 



41 



41 



34 



3 

 16 



37 

 39 

 40 



Triturus 



32 

 31 



^2 



23 

 26 



32 

 29 

 29 

 26 



35 

 53 

 26 



36 

 29 



50 

 43 

 21 



21 

 36 



jersoy-iiajium controls are available. They indicate a slight hermaphrodite 

 tendency, at least in some of the varieties. 



Single newts and salamanders metamorphose at the age of from four to six 

 months, and sex differentiation starts during the second month, when the 

 larvae are from 22 to 30 mm. long. Tiger salamanders progress somewhat faster 

 than /I. maculatum, A. je^ersonianum, and T. torosus, though time differences 

 are not sufficiently large to enter as an important factor into the consideration 

 of the experiments reported in this paper. 



At the metamorphosis stage, the gonads are largest in A. tigmium and 

 jeQersonianiim , smallest in T. torosus (compare the cross sections shown in 

 fig. 8m, ^T, and 12/). Triturus torosus differs from the salamanders in being 

 strictly gonochoristic. No trace of hermaphrodism has yet been found in any 

 controls of this species (McCurdy"). On the other hand, in the salamanders, 



\ 



