TRANSACTIONS OK SECTION D. 787 



Oniscus aseltiis, the common brown slater, resembles Lt(/ia in the general 

 structure of its respiratory organs. It has, however, a curious additional breathing- 

 organ at the outer edge of each exopodite. This is scooped out beneath to form a 

 very thin-walled air-chamber. 



Porcellio scabef 13 noteworthy on account of the presence of whitish patches upon 

 the first two pairs of abdominalexopodites. These are caused by minute air-tubes 

 excavating the exopodite. It is interesting to find an independent acquisition of 

 air-tubes, although they exhibit none of the perfections found in insects' tracheae. 

 The habitat of Oniscus is distinctly damper than that of Porcellio. 



A large number of experiments were tried with these two kinds of woodlice 

 under very wet and very dry conditions, the results being that Oniscus outlived 

 Porcellio when submerged ; but Porcellio easily outlived Oniscus under dry con- 

 ditions. 



Several other genera of woodlice were examined, their habitat noted, and a 

 large number of similar experiments conducted, with the result that the common 

 genera can be arranged in an ascending series from a wet to a drier habitat, and 

 the structure of the respiratory organs shows corresponding modifications ; in fact, 

 the one is the result of the other. 



These results can be tabulated thus : — 



Habitat. Isopod. Eespiratory Oegans. 



Aquatic .... Asellus aquaticus . . Gills. 



High-water line . . Ligia, oceanica . . Gills, with stouter exopodites. 



Wet grass . . . Tricho7ilsvus pusillus . Ditto. 



•p • v, 1 f Oniscus asellus ."[ Gills, with special air-chambers 



*^ P ^ ■ "1^ Phlloscia muscarum . | at edge of exopodites. 



T, • 1 r> 77- J. r Air- tubes iu two pairs of exo- 



Drier places . . . Porcellio scaber ' ■] d'i 



Dry places (often very 1 ^^^^^^^.^^.^ ^^„^ ^.^^^ ^^ f Ditto. wi:th power of rolling 

 dry) . . . .; -^ L up. 



Cylisticus convexus has air-tubes in five pairs of exopodites, and can also roll 

 up ; but this has not at present been found in sufficient numbers to verify by 

 experiment its place in the above list. 



The author is undertaking further inquiries into the bionomics of this group. 



Report on the Occupation of a Table at the Zoological Station, Naples. 



See Reports, p. 297. 



7. Report on the ' hidux Animalium.'-^^ee Reports, p. 297. 



8. Report on Experiments in Inheritance. ^^qq Reports, p. 298. 



9. Report on the Fauna of the Lakes of Central Tasmania. 

 See Reports, p. 302. 



10. Eighteenth Report on the Zoology of the Sandwich Islands. 

 See Reports, p. 301. 



11. Interim Report on Zoology Orgdili-Ution. 

 1908. 3 u 



