590 
Cestodes from Selachians 
External characters. Total length 100 mm.; number of' seg¬ 
ments ca. 70. Head provided with two oval bothridia, measuring 0-33 x 
0-27 mm.; connected along their anterior half to the head axis, directed 
antero-laterally, very movable in life; with two openings anteriorly, 
from which long proboscides protrude. Neck fairly long (3 mm.); 
breadth 0-13 mm. just behind the head, 0-1 mm. (minimum) anterior 
to proboscis sac; proboscis sac region slightly swollen, spindle shaped 
(0-5 X 0-2 mm.), continuous behind with the first segment (0-1 mm. 
broad); anterior 20mm. of strobila, comprising ca. 20 segments, is 
very slender and delicate in texture; the segments then gradually 
lengthen and widen proceeding backward, the last segment being 
largest. The dimensions of various parts of body are given below 
(in mm.): 
Probosc. Ist 6th 20th 40th 45th Last 
Bothrid. Neck sac segmt. segmt. segmt. segmt. segmt. segmt. 
Length 0-33 3 0-6 0-36 0-7 1-6 1-4 1-5 2-9 
Breadth 0-27 0-1—0-13 0-2 0-1 0-1 0-2 0-6 1-2 1-9 
Segments, always much longer than broad; anteriorly along the 
strobila the segments are broadest at their posterior borders whilst 
in the posterior region of the strobila they are broadest in the middle; 
each segment bears pointed triangular flaps postero-laterally projecting 
from its posterior border. 
There are usually six flaps per segment but a few anterior segments 
bear two or six, where they bear two the flaps are small, one projecting 
on each side of the body; further back, four small secondary flaps 
appear dorsally and ventrally to the primary flaps; the flaps gradually 
increase in size. At the 20th segment the secondary flaps are nearly 
as large as the primary ones, then all six flaps increase equally in size 
caudally, reaching their maximum dimensions (0-55 mm.), at the 40th 
segment. In a few segments, following upon the 40th, the flaps are of 
uniform size, after which they shorten gradually and become smaller 
and obtuse. Genital openings lateral, irregularly alternate. 
Genital organs. Testes distorted oval or elliptical; scattered 
laterally in medullary field ; five to seven or more testes visible in cross 
section of the segment; most testes usually in the aporose half. Cirrus 
pouch large, elongated pyriform in shape, extending beyond middle of 
segment; occupying nearly all the porose half of the medullary field, 
leaving the narrow space at its ventral side where the vagina runs 
transversely parallel to the pouch; with thick muscular wall. Vas 
deferens entering the pouch basally, is narrow and strongly coiled in the 
