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specimens and therefore a normal structure, probably the genital 
aperture. If the latter was true then the worms could not belong to 
the species aegypliacus, for in this, the genital aperture is placed 
immediately behind the cephalic cone, at the very base of the 
projecting edge of the disc. 
A close microscopical examination of the three specimens kindly 
given to me by Dr. STEPHENS has confirmed this presumption ; the 
parasites represent a new and at the same time a true member of the 
genus Gastrodiscus. It appears superfluous to give a description ot 
its internal structure here, for this would mean nothing but a second 
description of the structure of Gastrodiscus aegypliacus. It may 
therefore suffice to point out the differences between the two species 
They are chiefly given in the position of the genital aperture and the 
extension of the yolk-glands. The former has already been men 
tioned ; it is a circular or transversely oval opening about 03 nun 
wide, and leads into a genital atrium of 03 mm. in cross diameter, the 
muscular wall of which is of considerable thickness and much more 
conspicuous than in the African species. 1 he floor of the atrium is 
again raised in the shape of a conical papilla on the top of which the 
male and female genital ducts open close by one another in minute 
pores. The yolk-glands show a richer development than in Gastrod. 
aegypliacus. In this species, it will be remembered, they are located 
in the ventral half of the body, between the intestinal caeca and the 
free margin of the disc, and it is rather exceptional to find some 
folliculi extending below the caeca into the space between these and 
the median line of the body. In Gaslrodiscus secundus, the yolk-gland- 
trespass on the intestinal caeca in such a manner that their loosely 
grouped follicles occupy, in the ventral half of the body, all the space 
left free by the other organs. A minor difference is afforded by the 
size of the suckers. The oral sucker which, in Gastrod. acgyptiacu >, 
presents a cross diameter of o - 8 mm shows, in G. secundus , a diameter 
varying, according to the size of the specimens, from 035 to 0‘65 mm.; 
the posterior sucker, in G. aegypliacus about 2 mm. wide, in 
G. secundus scarcely reaches 1*2 mm. in size. The uterus, in the body 
of the new species, principally takes the same course between the 
organs as in G. aegypliacus , but, although it is, in the two larger 
individuals at my disposal, thickly filled with ova, it seems that it does 
not form so many secondary loops as in the older species. The ova 
