[19]  ENTOZOA OF MARINE FISHES OF NEW ENGLAND. 471 
arounded knob. (Plate ILI, 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"; 
breadth of posterior edge, measured from tip to tip of the reflexed bor- 
der, 2.1™™; breadth of posterior, exclusive of reflexed border, 1.7™™, 
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 of living, active specimens 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 bothriaincessantly 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.) Theremaining 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 
