F. J. Meggitt 
47 
its outline, i.e. at every junction between two proglottides they curve 
towards the interior, to bend outwards again directly the junction is 
passed: their course is therefore like a spiral in one plane. Near the 
posterior border of each proglottis, the two dorsal vessels and the two 
ventral ones communicate by transverse commissures: the commissures 
have the same diameter as their respective longitudinal vessels. There 
are not, as far as could be ascertained, dorso-ventral commissures 
connecting the dorsal and ventral vessels of the same side. In the 
scolex, the dorsal and ventral vessels have the same diameter, 0-0056 mm.: 
more posteriorly, the ventral vessel increases greatly in size while the 
dorsal gradually diminishes, until in proglottides in which the genital 
organs are mature there is only a ventral vessel, the dorsal having 
completely disappeared. The ventral vessel continues to increase in 
size as far as the posterior end of the strobilus, attaining a size of 
0-18 mm. by 0-08 mm. 
In the scolex, the four vessels empty into a circular commissure 
(e.c.) just posterior to the rostellum and anterior to the suckers: from 
this, several branches run to the rostellum. At the level of the posterior 
third of the suckers, each longitudinal canal gives off a branch to the 
posterior border of the corresponding sucker ( 5 .). In addition to this 
definite excretory system, numerous fine branches, too minute to be 
traced, radiate in all directions from the longitudinal vessel and the 
commissure, forming an elaborate and extensive plexus. 
Nervous System. 
The nervous system (Text-fig. 4) consists of two longitudinal nerve 
trunks, running the whole length of the strobilus and following its 
outline like the longitudinal excretory vessels, and a central nerve 
mass under the rostellum. Throughout their entire course, the longi¬ 
tudinal nerve trunks give off minute branches which disappear in and 
apparently fuse with the surrounding parenchyma. In the scolex they 
bend interiorly, passing internally to the suckers but externally to the 
excretory vessels. At about the anterior level of the sucker openings, 
the two trunks bend inwards and run transversely across the scolex to 
meet and fuse in the centre (b.). The transverse portion is much larger, 
but at the same time, less compact than the longitudinal trunks. Just 
posterior to this central “brain,” each longitudinal trunk gives off two 
lateral branches (s.n.) which curve anteriorly, transversely, and then 
posteriorly to the corresponding suckers. The central “brain” gives 
off at each lateral extremity an anterior branch {1.): this divides into 
