226 Proceedings of the Royal Physical Society. 
XX.—Variation in Ephyre of Aurelia aurita. By James W. Low, 
B.Sc., F.Z.8., Zoological Department, University College, Dundee. 
(With Figures.) 
(Read 22nd March 1920. Received 15th January 1921.) 
It has long been known that considerable variation in the number of radial 
canals, tentaculocysts, and other structures, occurs in Aurelia aurita. There 
is an extensive literature on the subject, references to which may be found 
in the papers by Browne, M‘Intosh and Hargitt, who have themselves done 
important work in describing, classifying and giving statistics of the various 
types of abnormalities found. 
It was suggested to me by Professor J. F. Gemmill that an enquiry 
into the point whether individual strobilz produced always normal ephyre, 
or similarly abnormal ephyre, might throw some light on the mode of 
origin of these variations. | 
The material on which the observations were made was obtained from 
the Dove Marine Laboratory, Cullercoats, Northumberland. The number 
of productive strobila examined was twenty-seven, out of a total of about 
forty, the remainder of which did not strobilate in the laboratory. Each 
strobila was kept in sea water and in a separate vessel, and the ephyre 
given off were collected periodically so as to obtain them as far as possible 
in the order in which they were produced from the strobila. 
My best thanks are due to Prof. Gemmill for many valuable suggestions 
and advice while carrying out the work. I am indebted to the Carnegie 
Trust for a grant towards expenses incurred in obtaining material. 
It will be recalled that a normal ephyra of Awrelia shows eight 
arms (four perradial and four interradial), eight tentaculocysts, four pairs 
of gastric filaments, and four perradial mouth tentacles in the form of 
lappets, separated by four (interradial) mouth angle grooves. 
Strobila No. 4 (see Table below) furnishes a case in which variation 
occurred, in different ephyree, in both perradial and interradial arms. Among 
the first batch of ephyre there occurred a ten-rayed form, which was due 
to doubling of two perradial arms. In the second batch from the same 
strobila, I found an eight-rayed form which showed “twin” tentaculocysts 
in one of the interradial arms, while in the third batch, besides normal 
forms, there occurred a nine-rayed form, due to doubling of one of the 
interradial arms. In strobila No. 6, all degrees of doubling of the interradial 
ss Cel ee 
