214 



THE ANIMAL PARASITES OF MAN 



absent ; single genitals in each proglottis ; genital orifices in the median 

 line of the ventral surface, the cirrus and vagina open into a genital 

 atrium ; the uterus is behind them ; there are papillae in the vicinity of the 

 genital atrium ; the testes and follicles of the vitellaria are in the lateral 

 areas, the former in the medullary layer, the latter in the cortical layer on 

 both surfaces and occasionally extending to the median line ; the ovary 

 is situated ventrally, the shell gland dorsally. The uterus is in the central 

 field and foifms a rosette. The eggs are operculated. 



i. Dibothriocephalus latus (L.), 1748. 



yn. : Tcenia lata, L., 1748 ; T. vulgaris, L., 1748 ; T. grisea, Pallas, 1796 ; 

 T. membranacea, Pall., 1781 ; T. tenella, Pall., 1781 ; T. dentata, Batsch, 

 1786; Bothriocephalus latus, Bren^fc, 1819; Dibothrium latum, Dies., 1850; 

 Bothriocephalus cristatus, Davain5Br874 ; l Both, balticus, Kchnmstr., 1855 ; 

 Both, latissimus, Bugn., 1886. 



Length 2 9 m. or more ; colour yellowish-grey ; after lying 

 in water the lateral areas become brownish, and the rosette of the 

 uterus brown. The head is almond-shaped, 

 2 3 mm. in length, the dorso-ventral axis 

 is longer than the transverse diameter ; the 

 head therefore generally flat, concealing the 

 suctorial grooves at the borders ; these 

 suckers are deep and have sharp edges 

 (fig. 139). The neck varies in length ac- 

 cording to the degree of contraction and 

 is very thin ; there are 3,000 to 4,200 

 proglottides and there may be more ; their 

 breadth is usually greater than their length, 



FIG. 138. Various chains 

 but in the posterior third of the body O f segments of a Dibothrioce- 



they are almost square, and the very P halus latus ( natural size )- 

 oldest are sometimes longer than they are 



broad. There are numerous testes situated dorsally and laterally 

 in the medullary layer ; the vas deferens (fig. 140) passes dorsally 

 in obliquely directed loops in the central field towards the front 

 and forms a seminal vesicle before its entry into the large cirrus 

 pouch. 



. The orifice of the vagina is close behind the orifice of the 

 cirrus pouch ; the former passes almost straight along the median 

 line towards the back, and widens into a receptaculum seminis 



1 Until recently this worm, which was understood to belong to a separate 

 species, was proved on examination by R. Blanchard ("Mai. Par.," 1896), to be 

 Dibothr. latus. Compare also Galli-Valerio, in C. /. B., P. u. I. (i), 1900, xxvii., 

 p. 308. 



