1911] Watson: The Genus Gyrocotyle. 371 



Gyrocotyle urna as described by Wagener and Lonnberg. The 

 distribution of spines may vary with age, though it has been 

 found constant in specimens of all sizes of G. fimbriata. It is 

 also possible that the non-appearance of the spines may be due 

 to action of reagents on preserved material. The figure given by 

 Wagener (1852) shows a very close approach to the pattern given 

 above as characteristic for G. fimbriata. The whole question of 

 distribution of spines cannot be settled until more material is 

 available. 



The question whether penis or vagina opens more anteriorly 

 is a difficult one. In specimens killed between glass plates, these 

 relations can be very easily distorted. On the other hand, in 

 specimens not killed thus, it is very difficult to compare the posi- 

 tions of the two openings, as they are on opposite surfaces of a 

 body too thick to be made transparent by clearing agents. The 

 specimens in my possession show the two openings at practically 

 the same level, with a small range of individual variation, depend- 

 ing upon the degree of extrusion of the penis-papilla. 



Not having specimens of G. urna for comparison, it has been 

 impossible to decide whether this form is really a distinct one, or 

 belongs to Wagener 's species. Until comparison can be made, it 

 will be referred to as G. urna (var. ?). 



III. BEHAVIOR OF THE LIVING ANIMAL. 



The shape of the body varies greatly in the living animal, and 

 also in preserved specimens. Wagener 's figures (pi. 48, figs. 84, 

 85) are the best in the literature, so far as giving a faithful re- 

 production of the appearance of the living worm. His figure of 

 the preserved specimen, on the other hand, resembles very slightly 

 any specimen that has come under the writer's notice. The 

 acetabular extremity of the living animal is extended into a long, 

 slender, cylindrical proboscis, along the sides of which the spines 

 above referred to are distributed. This part of the worm is in 

 constant motion. Posterior to the genital openings, in the region 

 of the lateral frills, the body is flattened, slightly convex dorsally. 

 Posterior to the uterus the lateral frills become less deep, and the 

 body less flattened. This " neck ' ' region can be very considerably 

 extended. On the posterior extremity is borne the rosette, of 



