KNOWLEDGE. 



[March 1, 1901. 



therefore, easy to them. Many species are found on 

 the marshy shores or ou the surface of the waters of lakes 

 and pouds. and quite a fair number will reward the re- 

 searches of the seaside entomologist. 



Several species of the genus Isotoma, for example, may 

 be found jumping about among the cast-up seaweed at 

 highwater mark. Some of these are of interest since they 

 occur indifferently in inland and sea-shore localities. 

 Isotoma belongs to the Entomobryidse — the most typical 

 family of the Spring-tails — characterised bv a well- 

 developed spring (borne on the fifth abdominal segment), 

 a very small front fore-body segment (prothorax). and a 

 clearly segmented hind-body. The species of Isotoma 

 are not scaly as many Spring-tails are. but are clothed 

 with numerous hairs, sometimes also with bristles. The 

 hind-body segments are equal in length or almost so. 

 Isotonui pahiffris (Miiller) is one of our commonest 

 Spring-tails, occuning among herbage in marshy places, 

 and by the edges of ponds. But this species may also 

 be found among seaweed, and a dark, violet-brown 

 variety, haunting the coasts of the Baltic, has been 

 named fuciroln by Di's. Renter and Schott.j This par- 

 ticular variety, however, is known to occur in Scotland 

 by inland bogs. Such indifference on the part of the 

 same insect to marshy or sea-shore surroundings is highly 

 instructive, for it shows us a Spring-tail of the land in 

 the act of establishing itself along the tidal margin. 

 Isotoma Ufforalis, described by Prof. Moniez.§ from the 

 French coasts of the Channel, is probably a form of this 

 species. " It is very common," he writes, '' under the 

 fucus which clothes the rocks uncovered at each tide. 

 It runs very quickly beneath this shelter, leaps with the 

 greatest ease, and takes refuge readily among the fronds 

 of seaweeds or the shells of barnacles, when it is dis- 

 turbed.' 



Fia. 1. — Isotoma maritima. Magnified 25 times. (*. spring ; 

 r. t., ventral tube), a, foot-claws j b, tip of spring, magnified llo 

 time'^. 



Another, much rarer Isotoma, 7. mnritimri. Tullberg 

 ^Fig. 1). fust discovered on the Swedish roast, 

 has lately been found both on the eastern and 

 western shores of Scotland by Mr. W. Evans.|l 

 The teeth of the spring in this species are veiy 

 long and slender; if the end of the tooth be 

 examined under the microscope, the thin pointed tip, 

 and the long stiff bristle characteristic of the species can 

 be made out (Fig. 1, I). I. maritima occurs on the shores 

 of the Baltic, the North Sea, and the French coast of the 

 Channel, but, despite its name, it is not exclusively a 

 maritime insect. It inhabits Bohemia, and the Bohemia 



1 H. Schott. 'Zur Svsteraatik und Terbreitung palfparctiseber 

 CoIIembola." Kongl Svensir. Alad. Eandl., ToL'SXT \o 11 

 1893, 100 pp., 7 pis. 



§ R. Moniez. " Acariens et Insectes marins dcs Cotes du 

 Boulonnais." Ser. SioJ. .V. France, Vol. II., 1890, pp. 324-6. 



G.H. Carpenter and W. Evans. '' The CoUembolaandThvsanura 

 of the Edinburgh Distriet." Proc. S. P/,i/s. Soc. EiHn Vol" XIV 

 1899, pp. 221-266, pis. Y.-VIII. ' , . . .. 



of modern geogiaphy, unlike that of Shakespeare's 

 " Winter's Tale," has no sea-coast. Here, it seems, we 

 have an insect, already almost restricted to the shore 

 line, but still lingering on in the heart of the continent. 



Two other scarce shore-haunting Spring-tails Imtomn 

 irii.<iiicauda, Tullberg. and I. Schbtti. Dalla Torre 

 (littoralu, Schott) (Fig. 2), offer a great contrast in form 

 to I. mtiritima, as their spring-teeth are remarkably short 

 and thick, and bear blunt, stumpy tips which' differ 

 somewhat in form in the two species (Fig. 2, //. c). /. 

 cramicauda is found on the coasts of Sweden. Finland, 

 the Shetland Isles, and northern France, while I. Schotti. 

 until its recent discovery at the mouth of the Elbe and 

 on the western Irish and eastern Scottish shores, was 

 known only from Finland, Sweden, and Spitzbergen. 

 Like Machilis maritima, therefore, these marine Spring- 

 tails tell us of a former coast line stretching northwards 

 from our British area, and I. Schotti yields eWdence for 

 the extension of this ancient shore far into the Arctic 

 seas. 



Fig. 3. — Isotoma Besehii, 

 magnified 20 times, a, foot- 

 claws ; b, tip of spring, mag- 

 nified 120 times. 



FiS. 2 — Isotoma ScTiotti, 

 magnified 20 times. a, foot- 

 claws: i, tip of spring, magnified 

 140 times; r, tip of spring of 

 /. crassicatifta, magnified 140 

 times. 



Still further light is thrown on these problems of 

 ancient geographj' by j'et another raie Isotoma, lately 

 found by Mr. Evans among wrack on the shores of the 

 Firth of Forth. Resembling the two last-mentioned 

 species in its short, thick spring-teeth, this one is easily 

 distinguished by its very remarkable spring-tip. 

 (Fig. 3. h.) Except for its single North British 

 locality, and its occurrence on the coast of New 

 England, its known range is altogether Arctic. 

 Like some other, more imposing animals, it has 

 received a different name from well-nigh every 

 naturalist who has seen it. Lord Avebui-y and M. 

 Stscherbakov described it almost simultaneous!}- in 1898 

 from Spitzbergen — the former as I. spitzhergeninsis, the 

 latter as I. nrrtira. Last year M. Wahlgren called speci- 

 mens from the lonely arctic islet of Jan ilayen, I. 

 janmaytnsiit. But it appears that Prof. Packard, so 

 long ago as 1873, had described the same insect from 

 Polaris Bay, Greenland, as I. Beselsi).'^ which is appar- 

 ently the name by which we shall have to know it. The 

 scattered points where this little insect has occurred 

 help us to trace oiir old continental coast-line north of 

 the Atlantic westward to American shores. 



•^ C. Ptliaffer. " Pie Arltisclien und Subarktischen Collemhola" 

 (in Romer and Si haudinn's • Fauna Arctica '). Jena, 1900. 



