SEA-FISHERIES LABORATORY. 301 



Linton found it in Mustelus canis in the Wood's Hole 

 region. 



This cestode is very small and not easily seen among 

 the mass of food debris usually filling up the spiral valve 

 of the hosts. In the part of the strobila following the 

 scolex the diameter is often no greater than that of a 

 human hair. The following measurements apply to the 

 largest of four specimens found in the two fishes 

 mentioned above : — 



Length of head : 0'34 mm. ; 



Greatest diameter of head : 0'32 mm. ; 



Length of hooks : 0*095 mm. ; 



Width of proglottides immediately succeeding 



head : 0085 mm. ; 

 Width of proglottides about anterior third of 



strobila : 0*16 mm. ; 

 Width of proglottides about midway between 



head and extremity of strobila : 0*19 mm. : 

 Width of proglottides about posterior third of 



strobila : 0'2 mm. ; 

 Total length of strobila : 50 mm. 



In spite of its extreme tenuity this worm is easily 

 recognized by the peculiar modification in shape of the 

 proglottides, and by the characters of the head. Each 

 bothrium is divided by two transverse costse so as to form 

 three loculi, of which the most anterior is the largest. The 

 costae are situated rather far back so that the two posterior 

 loculi are very small. Fig. 14 is a view of the head 

 showing one of the bothria in face, but when the head is 

 rotated through 45° so that two bothria only are seen, and 

 these in profile, the latter are then seen to project very 

 considerably, giving the animal a most characteristic 

 appearance. At the summit of each bothrium there are 



