Part III. 



The Anatomy and Physiology of the Organs of Respiration of Porcellio, 

 Cylisticus, Armadillidium, Ligidium and Oniscus. 



Porcellio scaber Latreille. 



1 he general external anatomy and relations of the gills of Forcellio have been -nell de- 

 scribed by several of the autbors above mentioned, especially Lereboullet. It will be sufficient, 

 therefore, in the present woik, as a prepai-ation for an accoimt of the histological anatomy of the 

 outer gills and the included corpora alba, to describe the outward appearance of a single gill. 

 The features presented by the inner surface of the first right outer gill of Porcellio scaber, male, 

 are as foUows: 



The general outline (Fig. 1) is that of a triangle with broadly rounded corners. Along 

 the anterior side which is slightly curved inwards is situated the articulatiou of the gill with the 

 basal Joint (Art.). The inner side which lies contiguous to the stylet along the middle line of the 

 body is convex outwards; the lower two-thii'ds of its margin is beset with about 15 stout hairs. 

 The outer and posterior side forms an irregulär line marked by a sharp angle directed inwards. 



The face of the gill falls into two parts: the general part, making up more than one-half 

 of the whole and the special part which includes the corpus album. The general part is marked 

 by dots which along the margin are aggregated into a broad continuous line and elsewhere are 

 scattered or irregularly grouped. The marginal line of dots lies immediately contiguous to the 

 chitinous wall of the gill at the junction of the inner and outer faces. 



The special part may be seen best by mounting a gill in water and examining under a low 

 power of the microscope with reflected light. In tlie outer portion is seen a whitish body presenting 

 the general appearance of a deuse clump of bushes (Fig. 1, tr.). The base of the bushy mass lies 

 toward the angle on the posterio-lateral margin of the gill and the branches are arranged radiately 

 arount the base terminating in minute twigs. By focussing at diiferent levels it becomes evident 

 that this body lies within the gill which in this region is much thicker than elsewhere. Since by 

 transmitted light the body appears dark , it may be inferred that it contains air. Fiu-thermore, 

 by pressing upon the cover-glass a bubble of gas may be seen to pass out at the angular inden- 

 tation on the margin of the gill. 



A portion of the wall of the gill overlying the white body shows very marked modifications 

 (Fig. 1, Gr. a). This portion has well detined boundaries, being included within a curved line, con- 

 vex inwards, lying at the surface of the gill, and two shorter curved lines, convex outwards, the 



