TAPEWORM PARASITIC IN THE STICKLEBACK. 119 
Musculature. 
The musculature of the body consists of circular and longi- 
tudinal muscles (already described) under the cuticle, and more 
powerful inner longitudinal muscles (PI. IT. fig. 12). These latter 
are arranged in bundles, which run in the outer layer of the paren- 
chyma and havea diameter varying from ‘008 to ‘0103 mm. (Bene- 
dict, 0015 to ‘(004 mm.) ; anteriorly they diminish in size, although 
in the scolex anteriorly to the suckers they occasionally have a 
diameter of -0092 mm. The single fibres of which they are 
composed are °0035 mm. dia. (Kraemer, :007) ; occasionally 
spindle-shaped nuclei, ‘0028 x -0092 mm., with a prominent 
nucleolus, ‘(0023 mm. dia., are to be seen, the long axis of the 
spindle being parallel to that of the fibre. In the body, and 
especially in the neck, large fibres pass dorso-ventrally between 
the longitudinal muscle bundles. According to Benedict, 
“a loose sheet of circular muscle-fibres weaves around the 
longitudinal bundles. Large fibres pass in a transverse direction 
between these muscle sheets. The divisions between the pro- 
glottides are formed by the interlacing of these fibres with 
similar ones which cross them at right angles, both sets being 
here much more complicated than in other regions.” He does 
not figure them, however, and they do not appear to be present 
in my specimens. 
The musculature of the scolex consists of prolongations of the 
inner longitudinal muscles together with scattered dorso-ventral 
and sagittal fibres. The suckers have equatorial, meridional, and 
inner radial muscle-layers ; they are covered by a continuation 
of the body cuticle, which is not absent, as Kraemer states, from 
their cavities. 
Kaucretory System. 
The excretory system consists of four main longitudinal vessels, 
two dorsal and two ventral, which run, internally to the longi- 
tudinal muscles but externally to the yolk-glands, from the scolex 
to open at the posterior end of the body. ‘They are not, as 
Kraemer states, of equal diameter, but are unequal, the 
two dorsal being ‘0045 x -0068 mm., and the two ventral 
"002 x 015 mm. In the scolex they end in a circular com- 
missure, ‘0023 mm. dia., just under the suckers (text-fig. 3). 
Outside their course in the neck is a system of fine canals 
forming a complicated plexus from which other fine canals lead, 
either to the exterior or to the four longitudinal canals. These 
“foramina secundaria” have, according to Kraemer, a swollen 
portion at their opening, while the opening itself is guarded by 
a wisp of hairs. I have never had the good fortune to see the 
dilatation, the canals apparently having a uniform diameter, 
‘0017 mm., throughout their entire course; the wisp of hairs 
also I have never seen, although the outer cortex at places 
presents rather a hair-like appearance. La Rue (11) states: 
“There exists a wide variation in the types of structures which 
