1911] Watson: The Genus Gyrocotyle. 379 



uterus is hard to estimate, the number of turns may vary with 

 the state of contraction, and certainly varies with age. I have 

 been unable to reduce this to definite measurements. From 

 Spencer's diagram it seems probable that the uterus occupies 

 more space in G. rugosa than it does in G. fimbriata, or, accord- 

 ing to Haswell, in G. nigrosetosa. 



5. Presence of hooked embryos in uterine eggs. This is a 

 character easily applied and apparently thoroughly critical. It 

 serves to set off G. rugosa from the rest of the genus. 



6. The relative positions of the openings of the penis and 

 vagina. This character is perfectly definite and, applied to ma- 

 terial not flattened under pressure when killed, seems trustworthy. 

 There is one possible source of confusion, in the fact that the penis 

 opening is on the summit of a papilla, very mobile and capable 

 of considerable extension. The vagina is fixed in position. In 

 case this papilla should be fully extended, the penis opening 

 might lie in front of the vagina ; while if withdrawn it would lie 

 well behind it. The same criticism might hold for medio-lateral 

 relations. The fact that G. rugosa, the only form in which the 

 penis papilla has been observed greatly extruded, is also the only 

 one in which the opening is definitely in front of the vaginal 

 opening, suggested this possible source of error. Spencer's figure 

 seems to point in this direction. 



7. Presence of an eversible cirrus, adapted to self-impregna- 

 tion. This arrangement has been reported only by Haswell for 

 G. nigrosetosa. It does not seem probable that only one species 

 of the genus possesses a type of cirrus adapted to self-impregna- 

 tion, especially when it is reflected that single individuals of all 

 reported species have been found repeatedly in their hosts. It 

 is strange that no eversion of the cirrus has ever been noted in 

 any except the one specimen of G. rugosa studied by Haswell, 

 and possibly in the one figured by Spencer. 



8. Spinules lining ejaculatory duct. This character is of 

 service in setting off G. rugosa from the rest of the genus; 

 spinules (interpreted by Lonnberg as cilia) have been observed 

 in the ejaculatory duct of G. nigrosetosa by Haswell, of G. urna 

 by Lonnberg, and in G. fimbriata by the writer. 



9. Shape of spines. The data on this point need revision. 



