i 74 Papers from the Marine Biological Laboratory at Tortugas. 



mounted material does not show as many details of structure as could be 



desired. 



14. Phoreiobothrium lasium Linton. 



Report U. S. F. C. 1886, pp. 474-476, plate iv, figs. 24-29. Report U. S. F. C, 



1887, pp. 819-820. Proc. U. S. Nat. Mus., vol. xx, p. 447. Bull. U. S. 

 F. C., 1899, pp. 272-273, 426, 427, 428. Bull. Bureau of Fisheries, vol. 

 xxiv, pp. 340, 343. 



One specimen was found in the spiral valve of the cub-shark (Car- 

 cJiarhinus platyodon], July 12. 



Dimensions, in life, in millimeters: Length 9.8; bothrium, length 0.50, 

 breadth 0.20; breadth of head 0.42, of neck 0.16, narrowing to 0.12 at a 

 distance of 0.35 from the head, then enlarging again ; first distinct segment 

 4.9 back of head, but indications of segments in front of this ; first segment, 

 length 0.35, breadth 0.22; last segment, length 0.84, breadth 0.36; length 

 of longer prong of hook o.io, of shorter prong 0.03. 



15. Thysanocephalum crispum Linton. 



Report U. S. F. C., 1886 (Phyllobothrium thysanocephalum), pp. 464-468, plate 

 n, figs. 1-12. Report U. S. F. C., 1887, pp. 823-824. Report U. S. F. C., 



1888, pp. 543-556, plates LXI-LXVII, figs. 1-43. Bull. U. S. F. C., 1899, pp. 

 271, 426. Year Book of Carnegie Institution of Washington for 1906, 

 p. 116. 



Found in what was presumably a tiger-shark (Galeocerdo tigrinus}. 



This shark was captured on June 2, before my arrival at the laboratory, 

 and the spiral valve was preserved in formalin. While the shark had not 

 been identified, the type of the spiral valve, the nature of the stomach con- 

 tents, and, particularly, the presence of this entozoan in great numbers, 

 both of large and small examples, all point to the tiger-shark as the host 

 (see pp. 164, 167). 



These worms were found to be very numerous, large and small together, 

 and still attached to the mucous membrane of the spiral valve. The folds of 

 the pseudoscolex are preserved expanded and are in an unusually fine state 

 of preservation. This condition is the result of the intestines having been 

 placed in formalin while the worms were still adhering to the intestinal 

 walls. Not only do the specimens exhibit the structure of the pseudoscolex 

 better than would have been the case if the worms had been detached before 

 they were placed in the preserving fluid, but they also illustrate the mode of 

 attachment of this singular worm to its host. When this parasite attaches 

 itself to the intestinal wall the minute head penetrates the mucous membrane 

 while the fimbriated folds of the pseudoscolex are spread widely, thus making 

 an adhering, and probably, at the same time, an absorbing organ. 



One of these scoleces was mounted in balsam. The diameter is 9 mm. 

 There are eight pairs of primary divisions of the pseudoscolex. These 

 are simply outgrowths of the anterior end of the strobile, being preceded 



