yO PROCEEDINGS OF THE NATIONAIj MUSEUM. vol.64. 



less serrate outline ; last proglottides thus far seen still broader than 

 long. Thus, in a strobile, 30 mm. in length, the proglottides near the 

 posterior end measured 0.56 in length, and 0.91 in breadth; in a 

 strobile 20 mm. in length, the length of the posterior proglottides 

 was 0.56; breadth, 0.70; in another which had been considerably- 

 flattened in mounting, length 30 mm., length of last proglottides, 

 0.63 ; breadth, 2.27. 



Reproductive organs. — The genital pores are irregularly alternate, 

 nearly symmetrical with respect to the dorso- ventral faces, and near 

 the middle of the length ; the cirrus is smooth, slender, with a bulbous 

 base; the cirrus-pouch is cylindrical and extends from the genital 

 pore, first forward to near the anterior margin of the proglottis, 

 then transversely toward the median line ; in an immature proglottis, 

 0.27 mm. in length and 1.33 in breadth, the inner end of the pouch is 

 0.49 from the margin ; it is 0.56 in diameter, and has coils of the vas 

 deferens, here quite slender, enclosed in the inner end. Voluminous 

 folds of the vas deferens lie between the inner end of the bulb and 

 the median line, on the dorsal side as far back as the level of the 

 ovary. The testes appear in sections as two layers, and fill all the 

 interior of the proglottis within the layer of vitellaria not occupied 

 by other genitalia. The vagina lies close to the cirrus-pouch, on or 

 near the posterior border ; from the level of the inner end of the pouch 

 to the middle line it is somewhat convoluted and lies beside the folds 

 of the vas deferens; at the median line it turns posteriorad and, 

 still more or less convoluted or sinuous, proceeds to its junction with 

 the germ duct. The ovary is about one-third the breadth and one-half 

 the length of a proglottis; in median sagittal sections it shows as 

 two divisions, one ventral and the other dorsal, both lobulated. The 

 shell gland, and the complex of germ duct, sperm duct, vitelline ducts, 

 and beginning of the uterus lie between the dorsal and ventral lobes 

 of the ovary. The vitellaria form an almost continuous layer im- 

 mediately adjacent to the body wall, being interrupted only in the 

 vicinity of the genital pores and the ovary. The uterus passes from 

 the shell gland as a comparatively slender tube along the median line 

 to near the anterior end of the proglottis, where it enlarges, becomes 

 subglobular, and opens to the exterior by rupture of the walls of the 

 ventral side of the proglottis at about the anterior third of the length. 

 In sections studied, the uterus was filled with a rather heterogeneus 

 mass of ova, germ, and yolk cells, from the vicinity of the shell gland 

 to the point of discharge of contents (fig. 84). 



r^/pc— U.S.N.M., Helm. Coll. 7726. 



Cestracion zygaena. 



On July 19, 1915, 1 examined the stomach of a hammerhead shark ; 

 the spiral valve of the same shark was examined by Dr. G. A. Mac- 

 Callum. 



