ox SOMK QUI'^KXSLAND 'I’HEMA'i'ODKS. 
367 
Excretory System. — The lai-ge branched vesicle opens 
into the proboscis chamber, Tlie pore is provided with a 
strongly developed sphincter which is capable of keeping it 
closed when the Hiiid of the vesicle is being forced into the 
finger-like processes of the proboscis. The vesicle divides into 
four wide bays anteriorly and each of these bays becomes 
gradually nai-rowed into one of the four main truuk vessels. 
Those placed laterally diverge as far as the testes^ round the 
outer sides of which they skirt, and then run forwards parallel 
to the sides of the body. Towards the anterior end they 
gradually trend inwards, and at a level just in front of and 
ventral to the intestinal fork they become joined in the form 
of a circular arch (fig. 26). All along their course they are 
provided with a number of wide side branches, regularly 
given off on the outer side and extending to the edge of the 
body (fig. f). These Ijranches do not anastomose with one 
another. The two vessels given off from the vesicle nearer 
the middle line pass the testes on the inner side and run 
forwards parallel to and within the intestinal limbs. They 
also give off a number of branches, but end blindly iu front 
near the intestinal fork, without forming a transverse anas- 
tomosis. The four main excretory vessels and the intestinal 
limbs are placed approximately in the same plane, so that they 
all appear together in the same horizontal (parallel to the 
ventral surface) section (fig. 26). 
Nervous System. — A pair of large cerebral ganglia are 
connected by a very thick commissure which crosses dorsally 
over the middle of the oesophagus (fig. 19). The principal 
trunks, in- the form of a pair of lateral nerve-cords, gradually 
diverge outwards towards the sides of the body, at the same 
time sinking ventrally so that at a point not far behind the 
intestinal fork they come to occupy a position immediately 
internal to the muscular layers of the ventral body-wall (fig. 
15). From the lateral trunks many small nerves are given 
off and are distributed laterally, inwards and dorsally. 
Reproductive Organs. — The genital opening is at the 
anterior eud, on the ventral surface, quite close to the sucker 
