272 The " Water-Flea " Scare in our City. [Sess. 



general and of the Edinburgh district in particular. These 

 observations are eminently useful at this time, when attention 

 is being so largely drawn to this little-studied group. -^ 



The spring-tails belong to the lowest group of the class 

 Insecta, namely, the Aptera or wingless insects — sub- division 

 Collembola. They are hatched from eggs, cast their skin, and 

 undergo no metamorphoses. Extremes of heat and cold seem 

 to have little or no effect on them. Their springing appa- 

 ratus, which is very curious, and found in no other insects, 

 consists of "a forked appendage bent under the body, and 

 which, when the insect leaps, is forcibly extended, so that it 

 strikes against the surface-film of the water, or against the 

 solid object on which it happens to be stationed, thus lifting 

 the body into the air." The largest of them are only about 

 one-eighth of an inch in length. Yet, with their grub -like 

 appearance, their leaping habit, their three pairs of legs 

 and one pair of antennae, they are rather uncanny-looking 

 creatures to the non-scientific observer. The" leaping appa- 

 ratus, possessed by most of them, gives the name Collembola 

 or " spring-tail " to this sub-division of the Aptera, in contra- 

 distinction to the term Thysanura, or " bristle-tail," applied to 

 the other and much smaller sub-division. 



As already mentioned, spring-tails are by no means uncom- 

 mon. According to Lord Avebury, one cannot shake a heap 

 of moss over a handkerchief without seeing them running 

 with agility and springing with considerable force. Of one 

 form — Isotoma fimetaria (Linn.), Tullb. — Messrs Carpenter 

 and Evans state that Dr E. S. MacDougall sent them a great 

 many, " obtained amongst sawdust at the Edinburgh Botanic 

 Garden," where, in March 1899, there are said to have been 

 " swarms." Of another form — Achorutcs viatimis (Linn.), 

 Tullb. — at Aberlady Bay, in September 1896, there are re- 

 ported by the same authors to have been " immense numbers 

 on the sands for a distance of several hundred yards on the 

 east side of the bay towards Gullane Point. And it is added, 

 "In some places there could not have been less than 20,000 



* See "The Collembola and Thysanura of the Edinburgh District," by George 

 H. Carpenter, B.Sc, F.E.S., and William Evans, F.R.S.E., in ' Proc. Roy. Phys. 

 Soc. Edin.,' vol. xiv. (1899) ; and "Some Spring-tails new to the British Fauna, 

 with Description of a New Species," by the same writers, ibid., vol. xv. (1904). 



