1911 1 Watson: The Genus Gyrocotyle. 381 



setosa, the presence of an operculum in uterine eggs must be 

 adopted as a specific characteristic of G. nigrosetosa. 



In addition to these characters which have been proposed and 

 found trustworthy, the writer suggests the following: 



1. The character of the folds of the terminal rosette, whether 

 simple or complex. This is correlated with the greater relative 

 size of the rosette ; but the fact that the size varies greatly and is 

 difficult to express in a ratio that could be applied to any speci- 

 men to be determined, makes the character of the folds them- 

 selves seem a more easily applicable test. The writer is convinced 

 that this character is constant in all stages of contraction, at all 

 ages, and after treatment with all the ordinary reagents. It 

 becomes unrecognizable only after decay has proceeded very far 

 indeed. 



2. The ratio between the distance from the opening of the 

 uterus to the tip of the acetabulum, and the distance from the 

 opening of the uterus to the level of the opening of the penis. 

 While these absolute distances vary enormously with the state of 

 contraction, a series of measurements shows that the ratio is 

 fairly constant about a mean characteristic of the species. 



TABLE I. 

 Eatios of Measurements of Position of Genital Pores in Gyrocotyle. 



G. Jimbriata G. urna G. rugosa G. urna (Wag.) G. nigrosetosa 



.4615 .266 .515 .333 .490 



.4500 .222 .582 



.4444 .200 .592 



.4444 .200 



.4375 

 .4375 

 .4295 

 .4295 

 .4295 

 .4290 

 .4000 

 .4000 

 .3809 

 .3333 

 .3333 

 .3333 



