EXPLANATION OF PLATE IN— continued. 



Fig. 6.— Transverse section of four gill-filaments of Mytilus, as seen 

 in a transverse section of the two laniellse of a gill-plate. The section 

 cuts two filaments of one lamella (the upper in the figure) throuf/h the 

 area of their ciliated junctions; the lower filaments are cut between the 

 position occupied by ciliated junctions. Obj. 8, oc. 4, Hartnack. 



Fig. 7. — A similar transverse section to that of fig. 6, but taken across 

 the region of interlamellar junctions. The interlamellar junctions are in 

 this case short; they are seen to be due to simple outgrowth of the 

 deep face of the filaments accompanied by concrescence. Obj. 8, oc. 4, 

 Hartnack. 



Fig. 8. — Portion of the descending and ascending limbs of a gill- 

 filament of Mytilus (filaments of the outer and of the inner lamella), 

 seen in the vertical plane at right angles to the surface of the lamellaj, 

 and showing two interlamellar junctions in a state of contraction, and 

 three pairs of epithelial prominences of the ciliated junctions. Obj. 4, 

 oc. 4, Hartnack. 



Fig. 9. — A bellows-like interlamellar junction in a state of partial 

 extension, from tne gill of Mytilus. Obj. 8, oc. 4, Hartnack. 



Fig. 10. — Diagram of a single gill-filament, with descending and as- 

 cending limb (filament of the inner and of the outer lamellse), from the 

 left outer gill-plate of Mytilus edulis. The diagram shows the grooved 

 apex or angle of the gill-plate, the hook-like termination of the free limb 

 of the filament, the position and number of the ciliated junctions (epi- 

 thelial prominences) and of the interlamellar junctions. The relative 

 breadth of the filament, as compared to its length, is exaggerated to the 

 extent of about twice the actual proportion. 



