STRUCTURE OF CLINOSTOMUM 



191 



and is frequently somewhat concave on the ventral surface. In 

 hving animals the posterior region of the body at times becomes 

 momentarily flattened and may thin out to a sharp lateral fin 

 but this is a merely momentary form followed by the thicker 

 form seen in the sections. The constriction of the body at the 

 level of the ventral sucker is shown in Wright's figure (79, fig. 1) 

 and in that of Linton ('98, pi. 44, fig. 6). It is also found in the 

 other species of the genus as can be seen in several of the forms 

 figured by Braun ('00). 



The dimensions of thirty-nine individuals were obtained from 

 worms mounted whole in balsam and drawn in outline with the 

 camera lucida. The measurements were taken both from mature 

 heron material and from bass worms. 



These figures correspond fairly with those previously published 

 except that the minimum one for length is the least thus far re- 

 corded. A part of the differences can doubtless be attributed 



TABLE 1 



Showing the length and width in millimetres of thirty-nine individuals of 



C. marginatum 



