Explanation of the Plates. 

 Plate I. 



Fig. 1. The tirst right outer gill of Porcellio scaher, male, as viewed froni tlie 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 sraber, taken in the direction of the line ss', Fig. 1. 



Gh., — chitine. 



Hy., — hypoderm. 



Hy. Nu., — 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. 



Gh., — 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. 

 B^ig. 7. Section of a portion of the respiratory tree at its base; tiie 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. 



