Part I. 
Introduction. 
Pile family Oniscidae is distinguished from the other families of the order Isopoda by the 
habit of living upon the land. The ajipendages of the abdomen -which in the aquatic isopods con- 
stitute organs for respiration in ivater subserve in the Oniscidae the function of resjiiration in aii'. 
In the systematic treatise of Budde-Lund ])u1dished in 1885, 37 genera and 282 species of 
land-isopods are descrilied. Of these 10 genera and 22 s})ecies are descrilied as found in Germany. 
Since the structural features of the organs of respiration vary Avith genera and suli-families 
ratlier than A\-ith species, in the present work I have studied a numlier of forms representative of 
genera, as followe: PorcelUo, Gylisticus, Armadillidiuiii, Liyidimi and Oniscus. I have used fresh 
material collected in the vicinity of Leipzig. 
The respiratory organs of the Oniscidae ai’c constituted in general liy the appendages of 
the first live segments of the alidominal region of tlie body. dTese appendages are of the morpho- 
logical type common in the Crustacea: each consists of a basal joint and an outer and an inner 
branch. The outer divisions are uniformly present in full number; Imt the inner divisions, as a 
rule, are lacking for the first two segments. 
The outer branches have generally been designated by authors as gill-covers. They form 
tAvo longitudinal roAvs of plates, constituting the ventral aspect of the abdomen. When at rest the 
inner margins of the plates meet at the middle line of the body and the posterior margins slightly 
overlap one another from in front haclvAvards, thus forming a closed, imlnlcated surface. This 
surface is convex transversly and slightly so from before hackAvards. It is broadest in front and 
gradually narrows backwards. 
This description, applicable to the females, requires a slight modification for the males. In 
this sex there are attached to the basal joints of the first and second pairs of the appendages the 
stylets of the reproductive organs. They lie along the middle line of the l)ody extending posteriorly 
to the extremity of the inner margin of the second pair of outer gills. The stylets, thus disposed, 
separate the inner mai'gins of the first and second pairs of outer gills. 
The gills are movable doAvmvards and side-wards by means of muscles connecting them 
Avith the basal joint. Those of each pair move simultaneously; and the series of pairs move suc- 
cessively from before backwards. The movements, as a whole, take jdace in rythmical order. 
In certain genera, including PorcelUo and Armadillidium, the first tAvo pairs of gills (in some 
species of PorcelUo all five pairs) jAresent peculiar modifications. To the eye these modified parts 
appear as whitish flecks and they have therefore been designated by some authors as corpora alba. 
