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THE ANATOMY OF AMPHIPTYCHES URNA. 145 
two join, a single duct coming from the median space filled with ova. A difference 
of structure has been noted above in the case of the ovaries of the two examples 
examined, containing embryos at different stages of development in the uterus, 
and a curious difference obtains also in the yelk glands of the two forms. In the 
one containing highly developed embryos the yelk glands, like the ovaries, are 
evidently providing a fresh supply of material in prospect of the next period of 
reproductive activity. Hach consists of a mass of cells, the outlines of which are 
somewhat more clearly marked than in the case of the ovaries, with large nuclei 
evidently undergoing division (Pl. 18, Fig. 10). The cells are remarkably similar to 
ova, but the relative size of the yelk masses and their definite superficial position 
renders them distinct from the ovaries. In the case of the form containing ova 
passing down into the uterus, the yelk glands are in a much more advanced stage. 
Kach is filled (Pl. 13, Fig. 9) with a mass composed partly of distinct yellow globular 
bodies, and partly of nucleated cells. These pass on until they reach the duct 
coming from the median space containing ova, and then with the latter pass on into 
the uterus, in connection with which their probable fate will be further dealt with. 
Uterus.—This commences at about one-third of the length of the body from the 
anterior end. At its point of origin it is connected with the duct from the ovaries 
and the yelk ducts, and as it passes towards the posterior end it very much enlarges 
and coils about from side to side, until finally it opens to the exterior at the base and 
to the inner side of the papilla (Pl. 11, Figs. 1 and 4, f.0.), on which the male opening 
is situated. Wagener observed the eggs passing out of the opening of the coiled tube 
whilst the animal was alive in water. 
The uterus is completely filled with embryos, the maturer ones lying nearer to 
the opening to the exterior. Two very different stages of development were 
‘observed. In three, as before mentioned, the ova had evidently not very long ago 
passed into the uterus, in fact, they were still in the act of passing in. The shells 
surrounding the ova were not completely formed in the upper part of the uterus, but 
when fully formed as they were, except in this special part, were so resistant that no 
stain had been able to penetrate to the embryo within. The latter had undergone 
but very little development. 
So far as can be seen there are no definite ‘“shell-glands” present; all the 
other structures connected with the reproductive organs could be distinctly made out 
by means of sections, and presumably shell-glands would have been able to be 
recognised if they were present as distinct and separate structures. In plate 18, 
figure 2, is represented a portion of the first part of the uterus, in which, evidently, 
the shells are being formed around the ova. In addition to nucleated cells, the uterus 
contains very numerous little drop-like yellow structures, which resemble exactly 
