J. Johnstone 
409 
much narrower duct runs towards the uterine canal and opens into the 
latter just as it turns round to run forward. 
The muscles of the proglottis. In addition to the muscles of the 
integument already described there are two series of longitudinal 
muscles and one series of dorso-ventral muscle fibres present in the 
segment. The longitudinal fibres are continuous with those which 
have already been described as originating in the proboscis bulbs. The 
latter fibres begin as four bundles which soon become gathered up so 
as to form twm flattened sheets respectively dorsal and ventral in position 
and running roughly parallel to the dorsal and ventral surfaces of the 
proglottis. At first these sheets are almost continuous but they soon 
begin to be split up into distinct bundles. As the vitellaria and testes 
develop the bundles become relegated to their definitive positions and 
run longitudinally between the vitelline glands and testes—or even 
among the follicles of the former organs. Each bundle consists of 
comparatively few fibres and these are always dorsal or ventral to the 
testes and never run among the follicles of this organ. The lateral 
margins of the proglottis are marked by the presence of the main canals 
of the excretory organs, and just dorsal and ventral to each lateral pair 
of these canals there is a bundle of longitudinal muscle fibres which is 
larger than the others. 
In the anterior parts of the strobila, where the segmentation is still 
incomplete, the longitudinal muscles run without interruption from the 
one proglottis to the next, but when the genital organs begin to 
be marked out this continuity of the longitudinal muscles ceases. 
Between every two adjacent segments there is a very narrow connecting 
region which seems to be composed of a tissue resembling dense paren¬ 
chyma similar to that which is found in the integument just beneath 
the basement membrane—it is indeed continuous with this part of the 
integument. The ends of the longitudinal fibres are inserted into this 
hardened parenchyma, and the terminal parts of the fibres themselves 
become tendinous in nature. The longitudinal fibres forming the 
integumentary muscle system are also inserted into this connecting 
tissue and are not continuous from segment to segment. 
The dorso-ventral muscle fibres are present in the young and mature 
proglottides but they appear to attain their fullest development in the 
latter: probably the}' become differentiated to the greatest extent as 
the proglottis becomes sexually ripe and acquires independent powers 
of locomotion. These fibres have been beautifully figured by Pintner 
(1880). They are smooth and band-shaped and the fibrous part runs 
Parasitology iv 
27 
