Part III. 
The Anatomy and Physiology of the Organs of Respiration of Porcellio, 
Cylisticus, Armadiliidium, Ligidium and Oniscus. 
Forcellio scaler Latkeille. 
The general external anatomy and relations of the gills of Forcellio have been well de- 
scribed l^y several of the authors above mentioned, especially Lereboullet. It will be sufficient, 
therefore, in the present work, as a preparation for an account 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 Forcellio scaler, male, 
are as follows: 
The general outline (Fig. 1) is that of a triangle with broadly rounded corners. Along 
the anterior side wliich is slightly curved inwards is situated the articulation of the gill with the 
liasal joint (Art.). The inner side which lies contiguous to the stylet along the middle line of the 
body is convex outwards; the lower two-tlurds of its margin is beset with about 15 stout hairs. 
The outer and posterior side forms an irregular 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 irregidarly grouped. The marginal line of dots lies immediately contiguous to the 
cliitinous 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 
pOAver of tlie microscope with reflected light. In the outer portion is seen a whitish body presenting 
the general appearance of a deuse clump of l)ushes (Fig. 1, tr.). The base of the bushy mass lies 
toward the angle on the posterio-lateral margin of the gill and the hi'anches are arranged radiately 
arount the base terminating in minute twigs. By focussing at dift'erent levels it becomes evident 
that this body lies Avithin 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. Furthermore, 
by pressing upon the cover-glass a huhlfle 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 AAliite body shows very marked modifications 
(Fig. 1, Gr. a). This portion has AA^ell defined 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 
