134 Proceedings of the Royal Physical Society. 



where these organs are not in perfect correlation, and he mentions, without 

 comment, in his tables (loc. cit., pp. 566, 567) two adults of that species which 

 are abnormal in this respect. The abnormality, however, is not very marked, 

 for one specimen has four gastric lobes (the normal number) and two oral lobes, 

 and the other has three gastric lobes and four oral lobes (the normal number). 

 This at least is perfectly clear — (1) there is a very intimate relationship 

 between the number of genital sacs or gonads and the number of oral lobes ; 

 and (2) such variation as is found in the number of oral lobes is small, and is 

 almost identical with the variation found in the number of genital sacs 

 (only about 2 per cent.). 



4. Variations in the Number of Branched Radial Canals. 



It is in the number and arrangement of the branched canal system that I 

 found the greatest variation. In a typical Aurelia at ephyra stage there are 

 eight simple, that is, unbranched canals. These eight primitive canals 

 undoubtedly become the eight branched canals of the adult. They stretch 

 from the stomach, of which they are really prolongations, to the margin of 

 the umbrella, and as they normally are placed at regular intervals they help 

 in making more obvious the animal's radiate symmetry. It may be taken as 

 proved that " larval variations are carried over into the adult through the 

 several phases of metamorphosis" (Hargitt, I.e., p. 555). For convenience, 

 it is customary to name the four branched canals situated opposite to the 

 genital sacs as Interradial Canals, and the other four, situated between the 

 gonads and opposite to the mouth angles, as Perradial Canals (Fig. 1). While 

 the branching is essentially of one type, it may be doubted whether two 

 specimens occur with identical branching. There is as great variation as in 

 the venation of the leaves of a tree. Thus it is that when we speak of 

 symmetry in an adult, we must consider it as applying (so far as the canal 

 system is concerned), not to the branches of the canals but to the canals 

 themselves. There is developed, even in immature adults, a single un- 

 branched canal, named the Adradial, between each of the eight canals already 

 mentioned. There are thus sixteen main canals, symmetrically placed to 

 each other, and to the central systems of the organism. 



There is a very definite correlation between the number of branched 

 radial canals and the number of tentaculocysts. Normally a single tentaculo- 

 cyst is found at the outer margin of each of the eight branched canals. The 

 relative position of these radial canals to each other, to the unbranched 

 canals, and to the genital and nutritive systems, is so clear that there is no 

 diiliculty in locating the eight tentaculocysts (Fig. 1). The protective 

 hood at the margin of the canal, as well as the peculiarly persistent character 



