STRUCTURE OF CLINOSTOMUM 201 



and deiisei-, so as to form a compact capsule for the support of the 

 parts beneath. 



There are certain cells loosely clustered together in a mass 

 which lies in the parenchyma in the region directly anterior to the 

 ventral sucker. They are shown in figs. 1, 3, 4 5 and 5. These 

 cells are oval, and measure 0.03 by 0.015 mm. The nucleus, which 

 lies near the margin of the cell, is clear and round and contains one 

 or more nucleoli and a few minute grains of chromatin. These 

 cells lie among those of the parenchyma but differ from them in 

 appearance, having no processes and no connection with the fibers 

 of the parenchyma. Each cell is sharply bounded. They also 

 have no connection with the surface, no processes can be traced 

 from them going off toward the surface and their long axes lie in 

 all directions. If they communicated with the surface the cell 

 bodies would point in that direction. There seems to be no doubt 

 that they are purely internal in their physiological action. They 

 are similar in cytological appearance in both bass and heron worms. 

 The cells contain a clear homogeneous material which has a 

 marked affinity for stains. 



The physiological significance of this organ is entirely unknown. 

 Looss recognized these cells in the immature worms from the 

 fish cysts. He suggests ('85, p. 46 of separate) ^'vielleicht sind 

 es die Anlagen von Driisen, die spater. . . erste ihre 



Funktion antreten werden." But this suggestion cannot be 

 accepted since the cells are identical in structure in the mature 

 worms. MacCallum's suggestion ('99, p. 700) that they are 

 parenchyma cells cannot be accepted, for they are not found out- 

 side of certain limits and parenchyma cells pervade all parts of the 

 body. The great number of these cells leads one to believe that 

 they are important. Their entire absence of connection with 

 other organs implies an independent function. It seems there- 

 fore most likely that they are concerned in some way in internal 

 secretion. 



Parenchymal muscles. The muscles of the parenchj^'ma are 

 very well developed in Clinostomum. The usual two sets are 

 found, (fig. 3) namely, the longitudinal muscles and the dorsi- 

 ventral ones. There are no horizontal muscles. As the longi- 



