140 Proceedings of the Royal Physical Society. 



much less for individuals of the same size. As far as possible uo account 

 was taken of any individual with a " variation " which was suspected to be 

 the result of an accident. Only a few had to be rejected on this account. 



For the reasons which have just been stated, it follows that there is often 

 a real difficulty iu determining whether a given individual, no matter how 

 normal it may appear to be, does or does not show radial symmetry. 

 Besides, it is practically impossible to measure the extent of departure from 

 radial symmetry in some of these tiny organisms. For in the process of 

 capturing, preserving, and examining a collection of over a thousand speci- 

 mens, it may very well be that parts are damaged and symmetries upset. 

 But wherever it was found that any numerical variation occurred in any of 

 the organs considered, the question of symmetry was easily settled. It was 

 noted that most forms which had lost their radial symmetry had a bilateral 

 symmetry so far as the number and position of the main organs were con- 

 cerned. It is obvious that if there is any numerical variation in two sets 

 of organs in the same individual there can't be, as a rule, even bilateral 

 symmetry, unless there is perfect correlation among these organs. 



Let it be definitely stated that no attempt is being made to bring all 

 those examples showing numerical variations under one or even two types of 

 symmetry. What is clear is, that in a general way, a normal Aurelia aurita 

 shows radial symmetry ; that even where numerical variation is found in a 

 set of organs, there may still exist a bilateral type of symmetry ; that there 

 may be bilateral symmetry even when meristic variation is found in more 

 than one set of organs (provided they are perfectly correlated) ; and that there 

 are many cases where, keeping strictly to meristic variation, the organism is 

 unsymmetrical. 



In discussing this question of symmetry, Hargitt (op. cit., p. 565) says of 

 Romanes 1 — "In both the illustrations and the analysis of the facts, there is an 

 apparent effort of the author to reduce the variations to as few symmetrical types 

 as possible." Bateson found twenty-eight abnormal specimens out of 1763 

 adults which he examined for the number of gonads and oral lobes. " There 

 were therefore 1735 normals, 19 symmetrical varieties and 9 irregulars. It will 

 be noted not only that the symmetrical varieties are comparatively frequent, 

 but also that the several forms of irregularity were seen for the most part in 

 single specimens only " (Bateson, I.e., p. 429). It is not very clear from 

 this how Hargitt (I.e., p. 564) can criticise Bateson for " attempting to reduce 



1 lloiiianes, George J., "An Account of some new Species, Varieties, and Monstrous 

 Forms of Medusas," The Journal of the Linnean Society (Zoology), vol. 12, pp. 524-53] ; 

 vol. L3, pp. L90-194 (2 plans). 



