[19] ENTOZOA OE MARINE FISHES OE NEW ENGLAND. 471 



■a rounded knob. (Plate III, Fig. 12.) In some free segments with a less 

 rounded outline the shape is much like that of a steeple-crown hat with 

 a drooping, flexible rim. Length of a mature free proglottis 2.8 mm ; 

 breadth of posterior edge, measured from tip to tip of the reflexed bor- 

 der, 2.1 mm j breadth of posterior, exclusive of reflexed border, 1.7 mm , 

 tapering to an obtuse point in front. The bothria are four in number, 

 marginal, short-pediceled, unarmed, each provided with a single sup- 

 plemental disk (auxiliary acetabulum Diesing) on the anterior border. 



The bothria gf living, active sx^ecimens undergo such profound 

 changes upon being transferred from sea- water to fresh water that it is 

 necessary, in order to guard against mistakes, to give separate descrip- 

 tions for each condition. 



If allowed to lie in sea- water, these worms continue active for several 

 hours. Some, after lying for twenty-four hours in sea-water, were still 

 quite active, moving their bothria incessantly and alternately contract- 

 ing and elongating the body and throwing it into irregular kinks and 

 folds. The bothria are extremely mobile. They are usually hollowed 

 out or boat-shaped on the face, bounded by a thickened rim or border 

 which merges into the auxiliary acetabulum in front. In a resting po- 

 sition they are oval in shape, more or less narrowed in front and 

 rounded posteriorly. Locomotion is effected by thrusting the bothria 

 forward and attaching the face as a sucking disk to the surface over 

 which the worm is moving, and thus dragging the body along. The 

 bothria are usually thrust forward in pairs, the two which would 

 stand diagonally opposite in a cross-section constituting a pair. They 

 are thrust forward bodily and at the same time become greatly elon- 

 gated in front. This attenuated part of each is frequently bent out- 

 ward at right angles, so that the two stand apart like a pair of recurved 

 horns. (Plate III, Fig. 11.) The remaining pair of bothria meanwhile 

 is some distance back of the forward pair and much contracted longi- 

 tudinally, the apex of each being a short distance behind the rounded 

 papillary apex of the head. Each bothrium when thrust forward and 

 attenuated is tipped by the auxiliary acetabulum, which forms a sort of 

 sucker. Each individual bothrium, while active, resembles in its mo- 

 tions the movements of a common leech. The resemblance is height- 

 ened by the auxiliary acetabulum, which has much the appearance and 

 is used in the same manner as the anterior sucker of some leeches. 

 Often the posterior ends of the bothria bend outward and forward 

 until they almost meet the recurved anterior ends. The under both- 

 rium was noticed sometimes adhering to the bottom of the watch-glass 

 in which the specimen was lying and spread out into a broad, thin, 

 circular disk. In this case all appearance of a thickened border to the 

 face of the bothrium was obliterated. Behind the bothria the head 

 contracts suddenly into a short, neck-like part, which is about the same 

 size and shape as the first segments, and, like them, is terminated by 

 four triangular lappets at each of the four angles. This latter feature 



