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401 
composed of dense parenchymatous tissue, and of fibrous and muscular 
elements, and is not definitely circumscribed but fades out into the 
surrounding parenchyma. Most of the muscle fibres take origin in the 
integument round the genital aperture and run longitudinally in 
relation to the long axis of the sac, but some of them do not run 
completely round the latter but pass out into the parenchyma, or are 
even recurved and are again inserted into the integument at a little 
distance away from the genital aperture. There are also transverse 
fibres which run completely round the sac, and these are strongly 
developed. In addition to these two series of fibres there are radial 
ones which originate in the outer wall of the cirrus and are inserted 
Distal 
Fig. 9. Diagrammatic horizontal section through a ripe proglottis in the region of the 
cirrus sac. The arrangement of the muscles is schematic. Mag. 100 dia. 
into dense parenchyma in the wall of the sac. Round the base of the 
genital papilla there is a strong development of the integumentary 
muscles so that a sort of sphincter is formed, and in this region the 
parenchyma is very dense. The longitudinal and transverse fibres 
appear to be nucleated but the cell protoplasm of these myoblasts is not 
very evident. 
The genital papilla is a raised part of the integument and subjacent 
tissues surrounding the opening of the genital duct. The latter 
does not open directly on to the summit of this papilla, but into a 
shallow pit. The terminal part of the genital duct is common to 
both male and female tracts, being formed by the junction of the cirrus 
and the vagina, and it is apparently only this common genital duct that 
can be everted. Evagination of the cirrus is produced by the pressure 
