98 
Variation in Aurelia Aurita 
An increase or decrease in the number of tentaculocysts usually leads to an 
asymmetrical arrangement of the canals, so that a tentaculocyst situated in a 
strictly adradial position may be traced by its canal to either the perradial or 
interradial system. 
Three diagrams have been prepared to illustrate the correlation of the radial 
canal system and the tentaculocysts. Diagram I. shows the arrangement of the 
canals and tentaculocysts in a normal specimen. There are four branched per- 
radial canals and four branched interradial canals which are separated by simple 
unbranched adradial canals. The branched canals are all of the same pattern, but 
shoAv a considerable amount of variation. 
A A 
P 
Diagram I. 
The normal arrangement of the radial canal system in a normal specimen. 
P, perradial. /, interradial. A, adradial. G, genital sac with gonad. S, stomach. 
1\ tentaculocyst. 
In the diagrams the oral arms are omitted (they are perradially situated) and also the tentacles 
which form a fringe round the margin of the umbrella. 
The normal type is seen at the top of Diagram I. (perradial). There is a 
straight canal running direct from the stomach to the tentaculocyst, and it gives 
off two opposite branches, each of which is subdivided into many branches, all 
entering the ring canal. There are many modifications of this type and several 
are illustrated in the diagrams. The lateral branches are often not opposite each 
other, and in some specimens the main canal looks like a branch from one of the 
lateral canals. 
The interradial branched canal is of the same pattern as the perradial. In 
some specimens it looks however quite different, but it is only a modification of 
