662 Sex in Parabiotic Twins 



that neither ovaries nor testes of the salamanders become much modified, 

 while the gonads of the newts suffer severely in all but one of the twin com- 

 binations. 



TJ}e maculatum-Triturus series (table i) is of particular interest becavise 

 here the antagonism is moderate enough to permit identification of the ge- 

 netic sex of the newt in every case. In combinations of female salamanders with 

 male newts (mac J-T ^), both twins have essentially normal glands (fig. 9). The 

 newt testes are not smaller than in single controls of corresponding develop- 

 mental age. The salamander ovaries are entirely normal in five of the six cases 

 of this group (see table 1). They contain numerous large ovocytes and spacious 

 ovarial sacs. In the sixth pair (mac-T,.), the left ovary is likewise normal, 

 while the right one has no open ovarial sacs. Instead, its medullary cords are 

 compact (fig. lomj, and in a few places, they contain even a few primary 

 gonia (fig. 10/77^,). However, at the same time, this ovary contains large and 

 healthy ovocytes, so that one hesitates to ascribe the deviation to the proximity 

 of the newt testes. Yet it may be significant that we deal here with the oldest 

 pair of this series (table 1). A delayed suppressive action of the Triturus 

 testes is, therefore, not excluded. In fact, it gains support from another case, 

 the first of the jeffersonianum-Triturus twins (jef-T^). This differs markedly 

 from the other pairs of the second series (table 2) but resembles closely the 

 mac-T pairs. Probably the salamander in this instance belongs to a racial 

 strain of marked hermaphrodite tendency, while all others are of more gono- 

 choristic type. At any rate, in this jef-T^ pair we find also newt testes of normal 

 size and salamander ovaries with some effects of inhibition (fig. 11). As in 

 mac-T,., the ovary which is located nearer the newt testes shows more degen- 

 erative changes in the cortex and has more medullary gonia than the other 

 one. These two cases, each the oldest pair in its series, present the only, and 

 certainly very meager, indication of a possible inductive influence coming 

 from the newt and affecting the salamander sex glands. 



In female-female pairs macJ-T 2)> the ovaries of the newts are small, re- 

 tarded, and of reduced fertility. In male-male twins (mac J^-T J*), the Triturus 

 testes are considerably inhibited and, therefore, much smaller than in the 

 mac 5-T ^ combination. Lastly, in the mac J'-T 5 combinations, the sala- 

 mander males completely suppress ovarial development in newt females (fig. 

 8). The gonads of the latter are nearly sterile primitive folds in which the 

 female character is barely recognizable. In short, of the reciprocal hetero- 

 sexual combinations, one (macJ-TJ^) shows the minimal, the other (macj^- 

 TJ) the maximal degree of interference and inhibition. In the unisexual 

 combinations, the gonads of the Triturus member are partially inhibited. 



In two instances (nos. 17 and 19), the maculatum members, which had been 

 partly resorbed, were without gonads; their Triturus co-twins were males with 

 normal testes. 



The jeffersonianum-Triturus and tigrininn -Triturus series are summarized 

 in tables 2 and 3. The sex glands of the newt are much more severely damaged 



