562 
Cestodes from Selachians 
Vagina: opens into the bottom of the genital cloaca antero-ventrally 
to the cirrus opening and runs straight in along the cirrus pouch, 
passing ventrally to both the lateral nerve cord and dorsal canal of the 
excretory system ; its inner end reaches the median line of the segment 
and becomes continuous with the oviduct. The vaginal wall thick, 
with structure similar to vas deferens. 
Ovary : consists of four lobes, lying at the dorsal and ventral margins 
of both halves of the medullary field, being united medially by narrow 
processes, forming an isthmus. The oviduct arises in the middle of 
the isthmus, runs ventrally, then posteriorly in a slightly winding 
course to unite with the inner end of vagina. The united canal 
runs dorsally to meet the shell gland, which is situated postero- 
dorsally to the isthmus. 
Uterus: lies ventrally and longitudinally in the median line; in 
gravid segments it occupies a large portion of the medidlary field. 
The connection of uterus and shell gland is not well seen in my sections 
probably owing to faulty preservation. 
Yolk gland: strongly developed, situated in both the lateral ex¬ 
tremities of the medullary field. It lies at the margin of the medullary 
field, and extends into it, occupying the space between the lateral 
nerve and the region occupied by the excretory canals. Each lateral 
end of the ovarian lobe comes into contact with the inner end of the 
yolk gland. 
Musculature: the longitudinal muscles are well developed; they 
occupy nearly all the cortical field; the muscular bundles are numerous 
and arranged radially. 
Affinities. I am inclined to identify this worm with Phyllobo- 
thrium lactuca van Beneden, although there are some slight differences 
between my description and that of the author of the species. The 
chief differences are (1) the smallness of the strobila, and (2) the short¬ 
ness of the gravid segments. P. lactuca is stated to measure 150— 
350 mm. or more in length and 2—5 mm. in breadth; it is much larger 
than my specimens, whose segments are always broader than long 
throughout the whole length of the body. But the last segments of 
P. lactuca are said to be longer than broad. Van Beneden described 
and figured a very long segment which is 12—15 x 4—5 mm. My 
specimens are shorter than this in total length (including the last gravid 
segments), but these differences may be due to post-mortem changes. 
These slight differences, I think, do not suffice to separate my form 
from P. lactuca. 
