Explanation of the Plates. 
Plate 1. 
Fig. 1. The first right outer gill of Porcellio scaher, male, as viewed from the inner or dorsal side. 
Tr., — the respiratory tree. 
Gr.a., — the grooved area of chitine. 
Ch., — chitine at the junction of the two faces of the gill. 
Art., — articulation of the gill with the basal joint. 
Fig. 2. Markings of the chitine on the inner face of the general part of the gill. 
Fig. 3 a. Section of the grooved area of chitine. 
Gr., — groove. 
Fig. 3 b. The grooved area of chitine. 
Gr., — groove. 
P.a., — polyginal area, showing markings. 
Fig. 4. Cross-section of the gill of Porcellio scaber, taken in the direction of the line ss'. Fig. 1. 
Ch., — chitine. 
Hy., — hypoderm. 
Hy. Nil., — hypodermic nuclei. 
PL, — pillar. 
B.C., — blood cavity. 
B.ch., — blood chamber. 
B.sp., — blood space. 
Op., — opening of tree. 
Cv.tr., — cavity of tree, 
Ed., — ridge of chitine. 
Fig. 5. Portion of the respiratory tree, showing terminations of the branches. 
Fig. 6. Section of a portion of the respiratory tree and the adjoining wall of the gill. 
Ch., — chitine. 
Hy., — hypoderm. 
Hy. Nu., — hypodermic nuclei. 
B. Sp., — blood space. 
W.b.c., — wall of blood cavity. 
Tr., — cavity of branch of the tree. 
Fig, 7. Section of a portion of the respiratory tree at its base; the section was taken parallel with the 
faces of the gill. 
Gr.ch., — grooved chitine. 
Bd.chm., — blood chamber. 
Op.tr., — opening of tree. 
Br.tr., — branch of tree. 
W.b.c., — wall of blood cavity. 
