190 HENRY LESLIE OSBORN 



chapter in the hfe history of our subject to very workable hnits. 

 More favorable conditions for a study of the point could hardly 

 be imagined. Professor Linton's communication also adds a rew 

 host and a new locality to our knowledge of the distributior of 

 this animal. 



The present paper gives an account of the organization of 

 Clinostomum marginatum. In justification of this when t\^o 

 accounts are already extant I may plead the fact that neither cf 

 them are fully adequate and in some points both are erroneous- 

 Clinostomum is a parasite of some of our most desirable game and 

 food fishes and it is especially obnoxious because it is lodged in 

 the edible portion of its host. In order to keep the paper within 

 reasonable size I have left out many histological items and it is 

 hoped that later, when certain points have received additional 

 study, a further account of the histology may be published. 



EXTERNAL FORM AND DIMENSIONS 



The outer form of this, as of most trematodes, is extremely 

 changeable. It has therefore seemed best to give a description 

 of the form and measurements of worms after fixation. There is 

 little difference in form and proportions of body between the late 

 immature stages from cysts in the fish and frog and mature worms 

 from the heron. The encysted worms appear to average very 

 little smaller. Figs. 1 to 4 enable one to obtain an idea of the 

 form of the animal. Fig. 1 is from a worm killed under compres- 

 sion, which, after carmine staining, has been mounted entire. 

 Figs. 2 and 4 are from horizontal and transverse series; they show 

 parts which are on different planes as if they were on the same 

 level and need to be checked by the transverse sections shown in 

 fig. 3. Fig. 3 shows transsections from seven levels, all drawn to 

 the same scale. They are from a series of about one thousand 

 sections and the accompanying number is that of the section in 

 the series, and shows, though only very roughly, the distance of 

 the sections from each other. 



The body is subdivided into two regions separated at the level 

 of the ventral sucker. Anteriorly it is almost cylindrical, its 

 cross section being an ellipse, posteriorly it broadens considerably 



