400 WILLIAM A. HASWELL. 



tliey are about 1 mm. in length. Each bothridium is so 

 directed that a line running along the floor of its cavity in 

 the direction of the long axis, and prolonged forwards, would 

 meet the median axis of the neck at an angle of about 45°. 

 The cavity is not divided or reticulated. At its anterior 

 narrower end, where its margin is lowest, each bothridium 

 bears a small circular accessory sucker. 



The last segment (fig. 2) is 5 mm. long and 2 mm. in 

 breadth in the preserved specimens ; relatively narrower in 

 the extended living condition. 



Separated segments are to be found in abundance along 

 with the entire strobila3, moving actively through the intes- 

 tinal contents. In the course of these movements the shape 

 undergoes constant alteration, the phases through which it 

 passes being comparable to those of a Ligula in its most active 

 condition. The anterior end becomes thrust sharply forwards 

 until the " head " becomes long and narrow and pointed, and 

 the " neck " constriction becomes more or less completely 

 obliterated. Then suddenly the anterior end becomes drawn 

 together and thickened to form a distinct rounded knob, 

 constricted off from the rest (fig, 3). The part behind this 

 " head " now becomes drawn forwards, the region imme- 

 diately following on the head gradually becoming thickened, 

 while the head itself becomes gradually retracted until it 

 nearly completely disappears, to become again thrust for- 

 wards as before. The effect of these movements is clear 

 enough. By the thrusting forwards of the narrowed head 

 end, the thick matter contained in the intestine is readily 

 penetrated, the subsequently formed knob at the anterior end 

 then forming a point d'appui, towards which the rest of 

 the proglottis becomes drawn forwards. 



These independent proglottides attain a relativc^ly con- 

 siderable size, the largest being about 11 mm. in length and 

 1'75 mm. in greatest breadth. 



Attention has been recently directed by .Liihe (13) to 

 isolated proglottides from Acanthias, in which there is a 

 distinct mobile '' head " sinn'hir to that above described, but 



