3IO THE ANIMAL PARASITES OF MAN 



former in the medullary layer, the latter in the cortical layer on both surfaces, and 

 occasionally extending to the median line ; the ovary ventral, the shell gland dorsaL 

 The uterus is in the central field, taking a zigzag course, and frequently forms a 

 rosette. 



Dibothriocephalus latus, L., 1748. 



Syn. : Tcenia lata, L., 1748; Tcenia vulgaris, L., 1748; Tcenia grisea, Pallas, 

 1796; Tcenia membranacea, Pall., 1781; Tcenia tenella, Pall., 1781; Tcenia dentata^ 

 Batsch, 1786; Bothriocephalus latus, Bremser, 1819; Dibothrium latum, Dies., 

 1850; Eothriocephalus cristatus, Davaine, 1874' ; Bothriocephalus balticus y 

 Kchnmstr., 1855; Bothriocephalus latissimus, Bugn., 1886. 



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

 water the lateral areas become brownish and the uterine rosette 

 brown. The head is almond-shaped, 2 to 3 mm. in length, the dorso- 

 ventral axis is longer than the transverse diameter ; the head, therefore, 

 generally lying flat, conceals the suctorial grooves at the borders; 

 these suckers are deep and have sharp edges (fig. 205). The neck 

 varies in length according to the degree of contraction and is very 

 thin ; there are 3,000 to 4,200 proglottids and there may be more ; 

 their breadth is usually greater than their length, but in the posterior 

 third of the body they are almost square, and the very oldest are not 

 uncommonly longer than they are broad. There are numerous testes 

 situated dorsally in the medullary layer of the lateral fields ; the vas 

 deferens (fig. 192) passes dorsally in transverse loops in the central 

 field anteriorly 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 ; 

 the former passes almost straight along the median line posteriorly,, 

 and widens into a receptaculum seminis shortly before its junction 

 with the oviduct ; the ovary is bilobed, in shape like the wings 

 of a butterfly, ventrally in the medullary layer ; the shell glands lie 

 in the posterior recess of the ovary; the uterus, forming numerous 

 transverse convolutions, passes ventral to the vas deferens forwards. 

 Eggs (fig. 207) large, with brownish shells and small lids, 68 /JL to 71 p 

 by 45 At ; the ovarian cell, which is already, as a rule, in process of 

 segmentation, is surrounded by numerous large yolk cells ; the 

 proglottids nearest the posterior extremity are frequently eggless. 



The eggs, which are deposited in the intestine and evacuated 



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 Dibothrio- 

 cephalus latus. Compare also Galli-Valerio, in Centralbl. f. Bakt., Path, und In- 

 fektionskr., 1900 (i), xxvii, p. 308. 



