no CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



phenomena connected with the egg-laying process. The 

 numerous individuals taken measure in a preserved state 

 from 3.5 millimeters by 1.5 millimeters to 18 millimeters 

 by 10 millimeters. All were sexually mature. 



It is an interesting fact that the largest individuals are 

 found only on large-sized fishes, and that to a certain ex- 

 tent the size of the parasite is proportional to the size of the 

 host. Just what the governing factors are in this case it is 

 difficult to imagine. It can scarcely be attributed to an in- 

 ability to retain a foothold when the scales are relatively 

 large ; and it is also unlikely that the host and parasite are 

 the same age, and that, for example, medium sized trema- 

 todes will acquire a large size months or years hence, when 

 the fish is fully grown. 



II. External Characters. 



The general surface of the body appears smooth, but in 

 reality is beset with exceedingly minute and short projec- 

 tions of the cuticle. Other cuticular elevations of much 

 larger size occur on the under surface of the posterior 

 sucker, especially on its posterior half, where they have 

 the form of low rounded knobs. In the lateral portions 

 these are arranged in rows, but in the median area of the 

 posterior half they are irregularly disposed. On the ven- 

 tral surface of the body, near the anterior end, is the 

 mouth-opening, in front of which are two sucking discs. 

 On the left side about the level of the mouth is the common 

 opening of the male and female reproductive systems. The 

 dorsal surface is devoid of any important obvious structures 

 except the excretory pores, two in number, which are 

 situated on either side of the median line near the anterior 

 end of the body (fig. 11, e). 



The anterior adhesive organs (fig. 11, a) are elliptical in 

 form, with their margins but slightly elevated, and accord- 

 ingly the disc area contains a relatively shallow depression. 

 Special radial and circular muscles are apparently absent; 

 a marginal membrane (Randmembran) is also wanting, and 



