They lie in the oiiter and posterior portion of the plates and Üw posterior margins of tlie sauie 

 plates present indentations. These mark the places where sniall lmb})les of gas pass out fron» the 

 interior of the corpus album when a gill is placed under water and pressure applied. The use of 

 tlie niicroscope is requisite for this demonstration. 



In the genus Oniscus the outer hranches of all the a])dominal appendages (the gill-covers 

 of authors) present also definite modifications but mcn-phologically entirely diÖerent from those of 

 Forcdlio and ÄrmadiUidmm. The outer and posterior portion of each gill is thinner than the rest 

 and is niarked l)y lines arianged in a radiate manner. To the eye these lines appear as glistening 

 whitish Spaces, suggesting the presence of Chambers containing air. AVlien an animal is placed 

 under water these spaces gradually disappear ; when the same animal is returned to air the original 

 appearance is gradually regained. 



The. inner divisions of the abdominal appendages are, excepting in Liyiäium, uniform in 

 structure and relations for all genera which I liave examined. They consist of three pairs of deli- 

 citte flattened sacks attached to the third, fourtli and fifth abdominal segments. They lie within 

 the corresponding outer divisions and share with them movement« through the muscles of the com- 

 mon basal Joint. 



These organs have been designated as gills by all authors. 



In Lüjidümi all hve of the inner branches of the appendages are represented. Those of 

 the tirst pair consist of thin plates resembling in general the outer divisions. The inner branches 

 of the second pair are rudimeutary gills. The other three pairs are identical in general features 

 with the corresponding parts in the other genera. 



