DIBOTHRIOCEPHALUS LATUS 



with the faeces, hatch in water after a fortnight or more ; the embryonal 

 integument (embryophore) of the oncosphere is provided with cilia ; 

 after bursting open the lid of the egg the oncosphere in its embryo- 

 phore (fig. 207) reaches the water and swims slowly about ; often it 

 slips out of its ciliated embryophore, sinks to the bottom and is capable 

 of a creeping motion; sooner or later it dies in the water. The 

 manner and means of its invasion of an intermediate host are still 



L J 



FlG. 204, Various chains of 

 segments of Dibothriocephalus 

 latus, showing the central 

 uterine rosette. (Natural size.) 



FlG. 205. Transverse sec- 

 tion of the head of Dibo- 



thriocephahts latus. 30/1. 



FlG. 206. Fairly mature proglottis of Dibothriocephalus 

 latus* The vitellaria are at the sides ; the uterus, filled 

 with eggs, is in the middle, also the vagina (the dark stripe 

 passing almost straight from the front to the back), and the 

 vas deferens (almost hidden by the uterus). Above in the 

 centre is the cirrus sac, and below the shell gland and ovary 

 are seen. 15/1. (From a stained preparation.) 



unknown ; yet we are aware that the larval stage (plerocereoid, 

 fig. 208), which resembles the scolex and may reach a length of 30 mm., 

 lives in the intestine, in the intestinal wall, in the liver, spleen, genital 

 glands and muscular system (fig. 209) of various fresh-water fish, 

 the pike (Esox lucius), the miller's thumb (Lota vulgaris), the perch 

 (Perca fluviatilis), Salmo umbla, Trutta vulgaris, Tr. lacustris, Thymallis 

 vulgaris (grayling), Coregonus lavaretus, C. albula (in Europe) and 

 Ouchorhynchus perryi (in Japan). The transmission of the plero- 

 cercoids from these fish to the dog, cat and man (Braun, Parona, Grassi 

 and Ferrara, Grassi and Rovelli, Ijima, Zschokke, Schroeder) leads to 



