MUSEUM OF COMPARATIVE ZOOLOGY. 125 
genital openings, n0, 20, one natural, the other partly cut away. The central cavity 
abovo the mouth is the stomach proper, from which radiate pouches, Sí”, more simple 
adherent above and below on ten radiating lines, as 
lds, 7, & The genital organs were wholly unde- 
ig compartments of the body- 
the 
than in Gorgonocephalus, and 
may be seen under the radial shie 
veloped, and there were to be found only the ten radiati 
savity, whose lining membrane, as in Gorgonocephalus, doubtless takes on 
reproductive function. They were continued from the genital openings, % 0, under 
the pouches of the stomach, and intercommunicated by a ring-tube 
and between 
mouth-tentacles ; 
round the mouth, sections of which are seen at of, Of. —1, 
d^, teeth. 
Fig. 6. 1. A vertical, radiating section through an arm, a little beside the median 
line, and a part of the disk of Astroenida isidis. The type is Astrophyton-like, with 
The stomach has pouches, St”, less folded and complex than 
Ophiuroid features. 
Where the stomach 
those above deseribed ; and it is quite free on the under side. 
proper folds back from and over the mouth-wall, the two adhere to form a ring-tube 
(perihæmal canal) just outside the stomaeh-sphineter, du. This and the want of 
attachments along the floor of the stomach are characters of Ophiurans. The ova- 
ries, 8, consist of egg-clusters, and lie in the body-cavity, into which penet rate the 
genital openings, as in Gorgonocephalus. — d, mouth-papillæ ; / section of mouth- 
frame ; 7, mouth-tentacles ; w^, passage for the nerve, bloodvessel, and water-tube of 
the arm ; w”, arm-bones. 
Fig. 7. 4. Ophiocreas cedipus, male. Base of an arm tipped a little from tho ob- 
server, with outer corner of the disk, whose side is cut away, while the integument of 
the arm is cut and folded back, showing a double-lobed spermary, ô, 6, whereof there 
is one on either side of the upper surface of the arm. The pleated floor of the stom- 
ach, St, St, is slit to expose the genital pouch, or bursa, below, which is an indenta- 
tion of the disk-wall, debouching by the genital opening, no. The spermary 18 En» 
closed by a thin continuation of the lining membrane of the disk, and at its inner 
end connects by a pore with the bursa. Inder the outer end of the radial shield, 7, 
may be seen a portion of the stomach, which adheres not only to the roof of the 
disk-wall, but also to the wall of the lower interbrachial space, so that the true body- 
cavity is reduced to a sinus over each arm, and to the closed ring-tube (perihæmal 
canal) about the mouth. 
CAMBRIDGE, February, 1881. 
