VARIATION OP TENTAOULOOYSTS OF AURTILIA AURITA. 249 



centages of abaormality are very close for nearly the same 

 number of specimens. It is probable that if a thousand adults 

 could have been obtained at Plymouth the percentage of ab- 

 normal forms might have been closer than 2 per cent, of the 

 ephyrse taken in 1894. The adult specimens were taken at 

 random out of large jars ; and it is interesting to note how 

 close the percentage of abnormality of each complete hundred 

 comes to the mean abnormality. The first hundred showed 



23 per cent., the second 22 per cent., and the third hundred 



24 per cent, of abnormal forms. An examination of the spe- 

 cimens does not show that any particular position on the 

 margin of the umbrella is favoured either by an increase or 

 decrease of the tentaculocysts. 



Eighteen specimens possess seven tentaculocysts, and in 

 eleven of these the missing tentaculocyst is a perradial one, 

 and in seven it is adradial. The presence of an extra tenta- 

 culocyst may either affect the symmetry of a single quadrant 

 or one half of the umbrella, and in a few cases by being very 

 close to another not even upset the symmetry. 



Ten specimens with nine tentaculocysts show that the 

 extra tentaculocyst is in one quadrant of the umbrella, and 

 thirteen specimens have one half of the umbrella containing 

 five tentaculocysts about equal distances apart, and the other 

 half possessing the normal four. Five specimens have eight 

 tentaculocysts occupying their normal positions, and an extra 

 one only separated from a normal one by a few marginal 

 tentacles. When the tentaculocysts exceed nine in a specimen 

 their position is by no means constant, and a different arrange- 

 ment occurs in almost every specimen. In some the tentacu- 

 locysts are about equal distances apart, and in others one half 

 of the umbrella contains the greater number. 



A few specimens have three tentaculocysts very close to- 

 gether, and usually separated by a few marginal tentacles. 



One specimen of an adult Aurelia has fifteen tentaculocysts 

 with the normal number of genital pouches and arms. This 

 exceeds the maximum number reached among the ephyrse. 

 !None of the adults have, however, either thirteen or fourteen 



