VARIATION IN THE JELLY-FISH AURELIA AURITA 27 



1000 small adults (just past the ephyra stage) taken from 

 the Clyde some years previously. 



( i ) On the number of Branched Radial Canals and 



Tentaculocysts. 



A normal example of Aurelia aurita has eight branched 

 canals stretching from the central stomach to the ring canal 

 round the margin of the umbrella. Four of these, the 

 perradial canals, lie between the gonads, and the other four, 

 the interradial canals, are placed opposite to the gonads. 

 At the outer end of each of the branched canals there is a 

 single tentaculocyst or sense-organ. As there is perfect 

 correlation between the number of branched radial canals 

 and the number of tentaculocysts, except in the case of 

 twin-tentaculocysts, in the following table the figures which 

 stand for the number of canals represent at the same time 

 the number of tentaculocysts. 



Number of Branched radial I Number of Branched radial 



specimens. canals. 



2 with 6 



i 7 



238 ,, 8 (normal) 



10 ,, 9 



13 I0 



4 ii 



specimens. canals. 



8 with 1 2 



i 13 



3 14 



o 15 



T 16 



Examination of these figures shows 43 or 15.3 per cent 

 of these 281 specimens of Aurelia aurita had either more 

 or less than the normal eight branched canals and eight 

 tentaculocysts. This percentage, while less than what 

 Browne 1 found among Aurelias from near Plymouth, is quite 

 in accordance with the percentage of abnormal forms I had 

 previously observed among small adults from the Clyde 

 (I.e. p. 131). It will be noted that the range of variation is 

 from 6 to 1 6 tentaculocysts and branched radial canals, and 

 that where departure from the normal occurs the numbers 

 tend to be higher. What is especially worthy of remark. is 

 that there is not, as might be expected, a regularly decreas- 



1 E. T. Browne, 'Variation in Aurelia aurita,'' " Biometrika," vol. i. pp. 

 90-108. 



