160 



ZOOLOGY. 



This worm is extremely rare in America, but is common in 

 Western Switzerland and Central Europe, and in the north- 

 western and northern provinces of Kussia, Sweden, and 

 Poland. It is sometimes twenty-five feet long, and nearly 

 an inch broad, with 4000 joints. The club-shaped head is 

 unarmed, and the first sexually mature segment is about 



Fig. 109. Male reproductive organs, with parts of the female of Bothriocephalus 

 latus. t, testicular follicles, only a part are represented ; ve, their excretory ducts ; 

 vd, vas deferens ; c, cirrus ; cb, sac containing the cirrus ; , uterus containing eggs ; 

 o, ovary ; gl, shell-gland ; e, water-vascular trunks ; v, vaginal canal. After Landois 

 and Sommer ; from Gegenbaur. 



the 600th from the head. Leuckart has suggested that 

 the young of this tape-worm originate in salmon and 

 trout. 



The sheep-hydatid is the larva of Tcenia ccenurus (Figs. 

 110 and 111), the adult infesting the dog. The presence of 

 one or several of the hydatids in the brain of the sheep pro- 

 duces the " staggers " or vertigo. The vesicle varies in size 

 from a pea to a pigeon's egg. It is bladder-like, filled with 

 a clear pale yellow albuminous secretion, with a great num- 

 ber of retractile papillae (Z), g), which are the tape-worm heads 

 connected by narrow stalks to the common vesicles support- 



