Variation in Aurelia aurita. 141 



the variations to ' symmetrical varieties,' " and for " regarding ' irregular 

 varieties ' as exceptional." All that Bateson seems to me to imply is that 

 even where radial symmetry has been lost, a large proportion of the abnormal 

 specimens still show another kind of symmetry, and that an abnormal form is 

 not necessarily therefore an asymmetric form. This, at least, is precisely what 

 I found. 



In this connection Mayer (op. cit., p. 4) remarks: "The abnormal forms of 

 Aurelia are peculiar in that they generally preserve the radial symmetry of 

 the disc, even though the usual number of segments be changed. Thus, 

 instead of being composed of quadrants, the disc may be made up of halves, 

 the animal possessing two genital organs and two oral lobes, 180° apart ; eight 

 radial canals and two marginal sense-organs. The symmetrical varieties appear 

 to be about twice as numerous as the irregular abnormalities. It is evident 

 that symmetrical ' sports,' or discontinuous variations of Aurelia, are 

 continually being produced, and yet the form of the species as a whole 

 remains unchanged." And again (p. 5), " It appears from an inspection of 

 Hargitt's figures that when radial canals are non-radially symmetrical in 

 arrangement, they show a decided tendency to be bilateral in arrangement." 



Hargitt figures some interesting examples of Aurelia fiavidula with 

 tentaculocysts adradial in position. It may be at once conceded that 

 whether a particular canal is adradial or not, is largely a question of the 

 relative position of branched canals to each other and to other organs. So 

 far as my examples are concerned, I did not once find an undoubted adradial 

 canal which showed branching, nor did I find a tentaculocyst (which is 

 merely a modified tentacle) that could not be associated with either a 

 perradial or an interradial canal. Just because adradial canals do not 

 normally have tentaculocysts, no detailed account is given of them. 

 Occasionally an individual was found with one or more adradials absent. In 

 such a case, as also in that where there is no perradial canal, the intervening 

 space is filled up by excessive branching on the part of the adjacent branched 

 canals. 



It is especially difficult to decide the question of symmetry of gonads and 

 genital sacs in small adults. The shape, position and size of the gonads, 

 their position in the genital sac as regards other gonads and as regards the 

 mouth (which is the centre of symmetry of the individual), have all to be 

 considered though they cannot conveniently be " measured." Specimens of 

 equal size did not have the gonads equally developed, and in a few cases one 

 or more gonads were poorly developed, or showed signs of degeneration, 

 compared with the remaining gonads in the same individual. Ehrenberg 

 records a single example with the gonads round the mouth so fused that 



VOL. XVIII. L 



