Tapeworms of Birds 
to the degree of contraction. The proglottides are all broader than long 
with the possible exception of the most posterior: in some of the speci¬ 
mens the last two or three proglottides are quadrangular. 
Musculature. The musculature of the strobila consists of an outer 
and an inner layer of longitudinal muscles, separated by an incomplete 
layer of circular ones. The outer longitudinal muscle layer consists 
of small fibres closely set together, the inner one of 18-20 (Clerc, 8) 
very much larger ones with large intervals between them. The fibres 
of both layers bend slightly towards the exterior in the centre of each 
proglottis. At the junctions of the proglottides is a sheet of numerous 
strong transverse muscles and weaker dorso-ventral ones. In the 
scolex, the longitudinal muscles are fixed to the suckers and rostellum, 
while some reach the apex of the head. The rostellum conforms to the 
Amoebotaenia type (8) with some exceptions. The inner axis of the 
rostellum is much smaller in proportion to the sheath and much more 
compact. The space between the two, instead of being filled chiefly 
with modified parenchyma, contains numerous muscles which serve to 
retract the inner axis of the rostellum. 
Excretory System,. There are the usual four longitudinal excretory 
vessels, one dorsal and one ventral each side of the proglottis. They 
bend outwards in the centre of each segment and inwards at its junction 
with its neighbours. The dorsal and ventral vessels of the same side 
communicate with each other by a slender dorso-ventral vessel at the 
posterior margin of each proglottis: posterior to the scolex there 
appears to be no communication between the two dorsal or between the 
two ventral vessels. With the exception of the scolex, the dorsal vessel 
remains the same width (0-007 mm. clia.) throughout the whole length 
of the strobilus, and does not disappear early in its course as in many 
species. The ventral vessel increases greatly in diameter as it goes 
posteriorly, until it is four times the diameter of the dorsal (0-028 mm.). 
In each proglottis the vessels give off numerous branches which run 
a short distance towards the margin and then appears to end blindly 
in the parenchyma. Posteriorly the vessels are situated one-sixth of the 
width of the proglottis from its margin, but more anteriorly this distance 
is increased to one-third, Just posterior to the scolex, each vessel 
(0-012 mm. dia.) runs outwards, nearly to the edge of the proglottis, 
the two vessels of the same side approaching closely to each other 
(PL XX, fig. 12, l.). Each then bends round to run almost exactly 
anterior and parallel to its former course, and just posterior to the 
posterior margin of the suckers. It does not reach as far inward as 
