26 ANNALS OF SCOTTISH NATURAL HISTORY 



recent years that it has come to be looked upon as a 

 " measurable " quantity. Scientists, no longer content with 

 vague statements as to certain variations being occasionally 

 or frequently met with in a species, now demand a definite 

 assertion as to the extent of the variation in a particular 

 character as well as the exact percentage of cases in which 

 it occurs. Although it may very readily be admitted that 

 at present it is not possible either to explain the causes or 

 to interpret fully the facts of variation, it is believed that a 

 record of the extent of variation in certain organs of an 

 individual is an aid to biological study. The field to be 

 examined is inexhaustible, for it is the world of organised 

 life. What is required in the meantime is an ample collection 

 of data bearing on variation ; interpretation would not then 

 be long delayed. 



The following is a very brief account of some variations 

 observed in the common jelly-fish, Aurelia aurita (Linn.). 

 This animal is familiar to all visitors to the sea-side during 

 the summer and autumn months, owing to the frequency 

 with which it is found stranded on the shore. In the quiet 

 bays round our coasts, shoals of this jelly-fish are often seen 

 swimming near the surface of the water or drifting gently 

 with the tide. There is nothing fish-like either in the 

 saucer-shaped appearance of a jelly-fish or in the character- 

 istic pulsating movements by means of which it propels itself 

 through the water. In the months of August and September 

 1908, Mr. R. Elmhirst of the Millport Marine Station 

 collected for me 281 specimens of Aurelia aurita, partly from 

 Loch Ridden and partly from Kilchattan Bay, in the Firth 

 of Clyde. They were placed as soon as captured in a 5 per 

 cent formalin solution, and so successfully were they pre- 

 served that, though not examined for many months, only a 

 few specimens were so damaged that they had to be rejected. 

 As the time of year of capture indicates, these examples 

 were all well-grown mature adults. They were examined 

 for the purpose of comparing such variation as they showed 

 in certain organs with the variation I had already found a in 



1 D. C. M'Intosh, 'Variation in Aurelia auri/a,' " Proc. Roy. Phy. Soc. 

 Edinburgh, 1910," vol. xviii. pp. 125-143. 



