746 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [28] 



5. Dibothrium plicatum, Rudolphi. 



[PI. in, Figs. 1-6.] 



Echinorhynchus xiphice, Gmelin, Syst. Nat., 3047. Zeder, Naturg., 162. Ru- 

 dolphi, Entoz. Hist., ii, 308. 



Bothriocephalus plicatus, Rudolphi, Synops. 136 and 470, PL in. 2. Breinser, 

 Icon., PI. xiii, 1 and 2. Creplin, Nov. Obs. 87, PL n, 12-14; Ersch. and 

 Grub. EucycL, xxxn, 297. Dujardin, Hist. Nat. des Helm., 614. Vau 

 Beueden, Mem. Acad. Belgique, xxxviii, 36. Olssou, Lund's Uuivers, 

 Arsskrift IV, 11, PL in, Fig. 66. Von Linstow Comp., Helm., 218. 



Bothriocephalus truncatus, Leuckart, Zool. Bruchst., I, 37, PL i, 13. 



Dibothrium plicatum, Rudolphi, Diesing, Syst. Helm., i, 591; Revis., Ceph. 

 Par. 243. Wagener, Nov. Act. Nat. Cur., xxiv, Suppl. 71, PL viii, 94, 95. 



This Dibothrium is peculiar to thecoramon sword-fish (Xiphias gladius), 

 having never yet been found in any other host. Following is the 

 description given of it by Diesing: 



Head sagittate, compressed truncate at the apex, with oblong, lateral bothria. 

 Neck long, somewhat terete, swollen at the base, segments very short, at length 

 longer, with the posterior margin crisp-undulate. 



I have referred to this species five specimens of Dibothria from the 

 rectum of Xiphias gladius. The head and neck of each of these para- 

 sites were completely buried in the walls of the rectum. The part thus 

 buried measured about 13 mm . The cavity in which the head and neck 

 were inclosed was, in each case, an enlarged cyst-like space filled with 

 transparent, watery lymph. These spaces were noticed on the outside 

 of the rectum, lying immediately under the serous membrane, and were 

 at first taken to be encysted larval cestods, but upon cutting into one 

 of them the inclosed head and neck, except in one case, to be noticed 

 further on, were observed to be attached firmly to the inner muscular 

 layer of the rectum. After cutting away the remaining tissue from the 

 enclosed necks they were found to be continuous with the bodies of 

 some large Dibothria which lay in the lumen of the rectum and were 

 attached to its walls. The color of the head and neck was bluish- 

 white, that of the body grayish-yellow. After removal from their host 

 the worms were placed in sea- water, where they at once contracted to 

 about one-half their former length, while, at the same time, they be- 

 came much broader and thicker, with the segments so crowded together 

 that only their posterior edges were visible. They then had assumed 

 the characteristic shape and appearance which is shown in the sketch 

 (Fig. 1). Before they had thus contracted they bore a close resem- 

 blance to D. mannbriforme (U. S. Fish Commission Keport for 1880, 

 pp. 45G-458, PI. i, Figs. 1-4). The length of one after thus contracting, 

 exclusive of the head and neck, was 54 mm , while its greatest breadth 

 was 12 mm . Another measured GG nnn in length, with a breadth of 7 nim 

 throughout nearly its whole length, narrowing abruptly, however, at 

 the last three or four posterior segments, which measured 2 mm in 

 breadth. 



