1889.] ON THE ATTACHMENT OF EMBRYOS IN AURGLIA. 583 



5. Note on the Mode of Attacliment of the Embryos to the 

 Oral Arms o^ Aurelia aurita. By Edward A. Minchin, 

 Keble College, Oxford. 



[Eeceived October 31, 1889.] 



(Plates LVII. & LVIII.) 



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 (ect.) externally, endoderm (end.) lining the 

 lumen of the groove internally, and between the two mesogloea (me*.), 

 which is very thick at the hottom of the groove. The margins of 

 the groove are produced into numerous "digitellse" (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 (b) 

 a little to one side of it. Figs. 4 and 5, Plate LVII., represent in 

 outline two more sections from the same series through the brood- 

 capsules a and b of figure 3, in order to show the way in which a 

 becomes closed off from the groove (fig. 4) and b 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 rf) 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 mesogloea between the two. In the smaller 



