Variation in Aurelia aurita. 



137 



Browne, in noting this, calls it a case of twinning of the tentaculocysts, and 

 adds " this is very rare and only occurred five times in 1000 adult specimens " 

 {I.e., p. 90). Hargitt also refers to these double sense-organs as " twin 

 rhopalia, several cases of which were found " {I.e., p. 555). These variations, 

 amounting to exactly 1 per cent., have not been included in the tables 

 already given, because in each case there is but one radial canal and but 



tt. 

 Fig. 2. 

 Example with twin-teutaeulocyst {tt.) on perradial eanal (p.c). 



one protective hood for the two sense-organs. The adjacent positions of 

 the tentaculocysts are such that it is impossible to decide which is the 

 additional one. They are well named twin-tentaculocysts. Their exclusion 

 from the tables given does not alter the number of abnormal forms, but 

 only the extent of the variation, since no case of twinning was found except 

 in individuals where there was independently an excess of the normal 

 number of tentaculocysts. The following Table (VI.) gives some details 

 of those examples with twin sense-organs. 



Table VI. 

 The Canal System of 10 Individuals with Twin-Tentaculocysts. 



Arrangement of 

 Branched Canal System. 



Number of 



Branched 



Canals. 



Number 



of 



Tentaculocysts. 



Number 



of 



Examples. 



Position 



of 

 Twins. 



Perradial 



Interradial 



Perradial 



Interradial 



Perradial 



Interradial 



Perradial 



Interradial 



Perradial 



Interradial 



2 2 2 1*) 



1 1 1 1 \ 



2 2 1* 2 



2 1 1 1 ( 

 12 2 1*) 



1 2 2 1 5 



2 1* 1* 1 



1 1 1 1 i 



2 12 1) 

 1 1* 1 1 | 



11 



12 



12 



9 



10 



12 

 13 

 13 

 11 

 11 



6 



1 

 1 

 1 

 1 



Perradial 



Do. 



Do. 



Do. 

 Interradial 



* Indicates position of twins. 



