584 
Cestodes from Selachians 
increases toward the middle portion of body, reaching a maximum of 
3—4 mm., and diminishing toward the posterior end; this length 
gradually increases toward the la^t segment, attaining a maximum of 
1-0—1-5 mm. Anteriorly the strobila is thin and smooth, posteriorly 
it is swollen and folded to make a tube. 
Genital openings lateral and irregularly alternate, situated slightly 
anterior to the middle of each segment. Uterine pores on the ventral 
median line. 
Musculature weakly developed. Excretory canals two per side, 
running just inside the yolk glands. 
Male organs. Testes numerous, situated antero-dorsally to female 
organs, oval or spherical, measuring 0-11—0-15 mm. Vas deferens 
much coiled on itself near the outside of the basal portion of cirrus 
pouch, entering the pouch it enlarges to the vesicle-like duct; its distal 
portion is straight and thick-walled. Cirrus pouch elongate pyriform, 
measuring 0-5 x 0-15 mm. basally and 0-09 mm. broad distally. 
Vas deferens and cirrus pouch surrounded by cell layer with distinct 
nuclei. Male duct with vagina crosses the longitudinal canals 
dorsally. 
Female organs. Ovary irregularly lobed, extending transversely 
between the longitudinal canals on either side in posterior part of seg¬ 
ment; lying mainly ventrally, but extending dorsally. Ovary united 
to oviduct by the so-called “egg-swallower” in the median plane. 
“Egg-swallower” subspherical, depressed antero-posteriorly, its wall 
with strongly developed radial muscle fibres surrounded by cell groups. 
Oviduct follows “egg-swallower,” its course is strongly curved dorsally 
to union with proximal end of vagina. Oviduct provided internally 
with minute spinules, surrounded by two cell-layers with well-defined 
nuclei. Shell gland spherical or shghtly flattened, measuring 0-2 x 
0-14 mm., dorsal to the ovary and on the same level. Yolk duct 
arising at centre of gland, running ventrally and passing posteriorly 
to ovary, then crossing ovary and bifurcating, both ducts running 
outward to meet the yolk glands. Yolk glands situated just outside 
lateral excretory canals. Vagina runs from its opening inward-straight 
to anterior edge of cirrus pouch; after crossing the longitudinal canals 
dorsally, it runs to median portion of segment, where it coils several 
times, and soon enlarges to form the seminal receptacle; the small duct 
runs dorsally and again bends ventrally to union with oviduct. Vagina 
surrounded throughout by cell-layer with well-defined nuclei. 
Host. Cynias 'tnanazo (Bleeker), spiral valve. 
