366 University of California Publications in Zoology. [ VOL - 6 



These two species occur in fish from the same locality, even 

 taken on the same trawl. Both species have never been found in 

 the same individual. G. fimbriata is the more abundant of the 

 two. 



II. GROSS ANATOMY OF GYROCOTYLE. 



The characteristics on the basis of which species are separated, 

 as given in the literature of the genus, are of various degrees of 

 usefulness and trustworthiness. This is due in great measure 

 to the manifold changes in form and appearance of the living 

 animal and of specimens preserved by different methods in all 

 stages of contraction and deterioration. Before they can be 

 intelligently considered, a brief description of the gross struc- 

 ture of the animal and of the external form and behavior of the 

 living specimen will be necessary. First, the orientation adopted 

 in this paper must be defined. The pointed acetabular end is 

 the anterior, the rosette or canal end the posterior. The surface 

 on which lie the uterine pore and opening of the canal is the 

 creeping surface and the one to which the animal returns in rest. 

 It is therefore ventral. The following description refers espec- 

 ially to G. fimbriata. 



The worm when alive and attached is almost translucent. 

 After detachment it becomes opaque, whitish-yellow in color, 

 decidedly deeper in tone in the marginal frills and the folds of 

 the terminal posterior rosette. The anterior end is not frilled, is 

 highly contractile, and in the living animal is in constant motion 

 (pi. 33, figs. 7-9). It consists of a very muscular acetabulum, 

 whose margin can be retracted somewhat, while the whole can be 

 drawn back into the body by the retraction of the longitudinal 

 muscles attached to the sucker. Posterior to the acetabulum, in 

 the median dorsal line, lies the opening of the uterus (ut. po., 

 pi. 39, fig. 42). Anterior to this, one-third of the distance be- 

 tween the uterine pore and the posterior margin of the aceta- 

 bulum, lie the vaginal opening (vag. op.), on the ventral surface, 

 and the penis opening (p. op.), on the dorsal surface. Both lie 

 almost on the margin, but the penis opening is the more mediad 

 and anterior to the vaginal pore. In the median third of the 

 body of the adult, the much coiled and distended uterus occupies 



