24 OSBORN. [Vol. XVIII. 



which, as his figure 5a, present considerable resemblance to these, 

 and in which he is able, not only to recognize an oval cuticular por- 

 tion located in a low papilla of the outer cuticle, but also a nerve 

 fiber which as here pierces the cuticle and then runs inwards to 

 connect with a nerve cell in the parenchyma. As his studies are 

 also on the trematodes, I think that it is reasonable to base on 

 them the identification of the cuticular structures of Cotylaspis. 



I. The Marginal Organs. 



Certain organs of problematical function have been recognized in 

 some of the Aspidobothridse called " marginal organs." They are 

 found in Cotylaspis on the margin of the ventral sucker at the 

 points where the .walls of the acetabula meet it (see Figs. 3, 4, 5, 

 7, 8). There is one of these organs at each such meeting point, 

 so that the total number of organs in one animal is ordinarily 

 twenty. They lie in a triangular space at the junction of the three 

 masses of muscular tissue, surrounded by parenchyma. In surface 

 views of the living animal, as the movements have favored it, I 

 have been able to see at the points indicated in Fig. 4 the minute 

 openings of these organs by which they communicate with the 

 exterior (Fig. 32). The organ consists of two distinct portions, a 

 lower one nearest the outer surface and a deeper portion above the 

 first. These two parts are both oval and of about the same 

 size, viz., about 30 ju long by 20 /u wide. The structure of the 

 two, as seen in sections stained with iron-haematoxylin, is very 

 different. The lower part has a distinct narrow central passage 

 lined with a continuation of the outer cuticle, which passage can 

 be seen in some sections to pass entirely through the outer 

 part of the organ and enter the upper part, though this is 

 not visible in the section from which the drawing is made, 

 owing to the fact that the organ curves. Beyond this nar- 

 row duct the wall of the lower portion is very thick and is com- 

 posed, largely at least, of muscle fibers, some of which are visible 

 in some of the sections attaching to the central passage below and 

 into the upper portion of the organ above. In addition circular 

 muscles can be seen surrounding the narrow duct. The upper 

 part of the organ is hollow, but its cavity is large and the wall 

 relatively thin. The cavity as here is a constant feature of this 



