1889.] ON THE ATTACHMENT OF EMBRYOS IN AURELIA. 5 
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5. Note on the Mode of Attachment of the Embryos to the 
Oral Arms of Aurelia aurita. By Epwarp A. Mincuin, 
Keble College, Oxford. 
[Received October 31, 1889.] 
(Plates LVII. & LVIITI.) 
Some little while ago, when engaged in dissecting a series of 
Aurelia aurita in the Morphological Laboratory at Oxford, I noticed 
that a great number of the specimens supplied had the oral arms 
covered with little knobs or swellings, which, though varying greatly 
in size in different specimens, were always, when present, quite 
visible to the naked eye. I was unable at the time to obtain any 
information as to the meaning of these appearances, and therefore 
proceeded to investigate them by cutting sections of the arms. I 
then found that the knobs were really little stalked capsules or 
pouches containing embryos of Aurelia, formed as evaginations of 
the wall of the groove running down the arm, and with their lumen 
communicating with that of the groove through the more or less 
narrowed stalk. This is readily seen from the annexed figures. 
Fig. 1, Plate LVIII., represents an oral arm covered with the 
brood-capsules, drawn about three times natural size. Fig. 2, 
Plate LVII., represents a transverse section of an oral arm which 
bore no brood-capsules, in order to show the structure of the arms 
—namely, ectoderm (ec¢.) externally, endoderm (end.) lining the 
lumen of the groove internally, and between the two mesogloea (mes.), 
which is very thick at the bottom of the groove. The margins of 
the groove are produced into numerous “ digitelle” (d.), finger-like 
processes of the ectoderm, containing a core of mesogloea and thickly 
covered with nematocysts. Fig. 3, Plate LVII., represents a trans- 
verse section from an arm which bore very few, and comparatively 
small, brood-capsules. Two capsules are seen on the left side of 
the figure, one of which (a) is cut through its stalk, and the other (4) 
a little to one side of it. Figs. 4 and 5, Plate LVIL., represent in 
outline two more sections from the same series through the brood- 
capsules a and 6 of figure 3, in order to show the way in which a 
becomes closed off from the groove (fig. 4) and 6 becomes bifid 
(fig. 5). Fig. 6, Plate LVIII., represents one side of a transverse 
section through an oral arm which bore numerous, and relatively very 
large, brood-capsules. Four of the capsules appear in the section, 
one of them (e) cut through the middle of its stalk, two others 
(c and d) just to one side of their respective stalks, and a fourth 
(/) so far from its stalk that it appears as if detached from the arm 
altogether. 
From these figures it is evident that the capsules are formed as 
simple evaginations of the walls of the groove of the oral arm. They 
are hence lined by endoderm internally and ectoderm externally, 
with more or less mesoglcea between the two. In the smaller 
