Part I. 

 Introduction. 



1 ho family Oniscidae is distinguished froiii the other faiuilies ol' tlie Order Isopoda l)y Üw. 

 babit of living upou tbe land. Tbe appendages of tbe aljdomuii wliich in tbe aquatic isopods con- 

 stitute Organs for respiration in water sul)serve in tbe Oniscidae tbe function of respiratiou 'in air. 



In tbe systematic treatise of Budde-Lund publisbed in 1885, 37 genera and 282 species ol' 

 land-isopods are described. Of tbeso 10 genera and 22 specios are described as foiind in Germany. 



Since tbe structiu al features of tbe organs of respii-ation vary witb genera and sul>families 

 ratber tban witb species, in tbe present work I bave studied a nnnil)er of forms repräsentative of 

 genera, as followe: Porcellio, Gylwüciis, ÄrmadülklitDii, LvjidmyH and Oniscus. I bave used fresli 

 material collected in tbe vicinity of Leipzig. 



Tbe respiratory organs of tlie Oniscidae are constituted in general liy tbe appendages of 

 tbe first five Segments of tlic a1)doniinal region of the l)()dy. These ajjpendages are of the niorpho- 

 logical type common in tbe Crustacea: each consists of a basal Joint and an outer and an inner 

 hranch. Tbe outer divisions are uniformly present in lull nurahor; l)ut tlie inner divisions, as a 

 rule, are lacking for tbe first two Segments. 



Tbe outer brancbes bave generally been designated Ijy authors as gill-covers. Tbey form 

 two longitudinal rows of plates, constituting the ventral aspect of tbe abdomen. Wben at rest tbe 

 inner uiargins of tbe plates nieet at tbe middle line of tbe body and tbe posterior margins sligbtly 

 overlap one anotber from in front backwards, tbus forming a closed, imbricated surface. This 

 surface is convex transversly and sligbtly so from before backwards. It is broadest in front and 

 gradually narrows backwards. 



This description, api)licable to tbe females, requires a slight modification for the males. In 

 this sex tbere are attacbed to tbe basal joints of tbe first and second pairs of the appendages the 

 stylvts of the reproductive organs. Tbey lie along tbe middle line of the body exteuding postcriorly 

 to tbe extremity of tbe inner margin of the second pair of outer gills. The stylets, tbus dis^josed, 

 separate tbe inner margins of tbe first and second pairs of outer gills. 



Tbe gills are mova])le downwards and sidewards l)y means of muscles connecting them 

 witb the basal Joint. Those of each pair move simultaneously ; and the series of pairs move suc- 

 cessively from before backwards. Tbe movements, as a wbole, take place in rytbmical order. 



In certain genera, including Porcellio and Ärmadillidiiim, the first two pairs of gills (in some 

 species of Porcellio all five pairs) present peculiai- modifications. To tbe eye these modified parts 

 appear as whitish flecks and tbey bave therefore been designated by some authors as corpora alba. 



