TARDIGRADA 183 



spines of E. africanus, and these cannot be protective ; while the commonest of all 

 species have no spines. 



In one direction the study of the variations of form among the Tardigrada is 

 important, although we may not see the causes of the variation or its value to the 

 animals. Through the various forms we can learn the affinities of the species, and 

 we may thus gain some knowledge of the history of the development of the group. 

 Thus the Tardigrada are brought into geological history, although their remains may 

 be scarcely known in the strata of the earth. 



It is an interesting fact in itself that so many Tardigrada have been obtained 

 alive from dried mosses. Although a few were studied while the mosses were fresh, 

 the great majority of the fifty species were got from mosses which had been dried for 

 a longer or shorter period, varying from a month or two to nearly three years. 

 This brings out strongly the power possessed by habitual moss-dwellers of sur- 

 viving long periods of drought. After being kept for a year perfectly dry the 

 number of animals which revive on being moistened seems no less than when the 

 moss has only been a short time dry. After a year the vitality rapidly diminishes 

 after three years a very small proportion of the animals survive. The duration 

 of their vitality is greatly affected by conditions. If there is a suspicion of 

 moisture, if enough to produce mildew, or even merely to cause a musty smell, 

 they will not live long. 



In the Antarctic some experiments were made in order to test the limits to the 

 vitality of water-bears. These are detailed briefly under the account of Macrobiotus 

 arcticus. 



BIBLIOGRAPHICAL LIST OF WORKS REFERRED TO IN THE TEXT 



Several others, which came too late to be inserted in their proper places, will be found in footnotes. 

 In the text the references to this list are made in figures in heavy type, enclosed in parentheses. 



1. CARLZON, 0., " Schwedische Tardigraden," Zool. Anzeig., Bd. 34, 1909, p. 137. 



2. DoYiRE, M. T., "Memoire sur les Tardigrades," Ann. des sci. nat., Ser. 2, Tom. 14, 1840, p. 269. 



3. EHBENBERG, C. G., " Diagnoses novarum formarum," Verh. K. Akad. Wiss. Berl., 1853, p. 530. 



4. " Mikrogeologie," Atlas, Taf. 35u, 1854. 



5. " Mikroscopischen Lebens in bis 20,000 Fuss Alpenhb'he," Abhand. K. Akad. Wiss 



Berl. (aus dem Jahre 1858), 1859, p. 429. 



6. HAY, W. P., "A Bear-Animal renamed," Proc. Biol. Soc. Washington, xix., 1907, p. 46. 



7. HEINIS, Fr., "Tardigraden der Schweiz," Zool. Anzeig., Bd. 32, 1908, p. 633. 



8. "Moosfauna der kanarischen Inseln," Zool. Anzeig., Bd. 33, 1908, p. 711. 



9. ,. ,. " Moosbewohnenden Rhizopoden, Rotatorien, und Tardigraden," Arch, fur Ilydrobiol. 



und Planktonkunde, Bd. 5, 1910. 



10. HUTTON, F. W., "Index Faunae Novae Zealandia:," London, 1904. 



11. MUKEAY, J., " Tardigrada of the Forth Valley," Ann. Scot. Nat. Hist. 1905, p. 160. 



12. "The Tardigrada of the Scottish Lochs," Trans. Roy. Soc. Edin., vol. xli., 1905, p. 677. 



13. "Tardigrada of the Forth Valley," 2nd paper, Ann. Scot. Nat. Hist., 1906, p. 214. 



14. "Scottish Alpine Tardigrada," Ann. Scot. Nat. Hist., 1906, p. 25. 



15- ,, " Tardigrada of the South Orkneys," Trans. Roy. Soc. Edin., vol. xlv., 1906, p. 323. 



