JOURNAL OF MICROSCOPICAL SCIENCE. 



EXPLANATION OF PLATE IV, 



Illustrating Mr. Peck's memoir on the Structure of the 

 Lamellibranch's Gill. 



The letters in all the figures have the following signification. 



fol. Filament of the outer lamella. 



HI. Filament of the inner lamella; the two being the descending and 

 ascending "limbs" of one and the same primitive filament. 



cj. Ciliated (interfilamentar) junctions. 



ep. Epithelial prominences which carry the cilia of the ciliated 

 junctions. 



iJj. Interlamellar junctions (subfilamentar outgrowths or excres- 

 cences which stretch across the interlamellar space, and unite 

 the descending and ascending limbs of a primitive filament). 



e. Epithelium. 



le. Lateral epithelium. 

 fe. Frontal epithelium. 



Ife!. Latero-frontal epithelium with long cilia. 



Ife". Second row of the same. 



Ifc. Latero-frontal cilia. 



he. Blood corpuscle. 



lac. " Lacunar " or " primitive mesoblastic " tissue (Gallertgewebe, 

 mucous tissue). 



ch. Chitinous layer (mesoblastic). 



sep. Septum formed by lacunar tissue. 



cav. Cavity of the filament. 



lat. Broad side of the filament. 



Fig. 1. — A part of three gill-filaments of Area, seen from the surface 

 of the lamella, showing large ciliated junctions, and focussed so as to give 

 a median optical section. Obj. 8, oc. 4, Hartnack. 



Fig. 2. — Transverse section of a gill-filament of Area, showing epi- 

 thelium, cliitin, cavity, and septum. Obj. 8, oc. 4, Hartnack. 



Fig. 3.- — A gill -filament, twisted so as to show its narrow and broad 

 sides, and general band-like form. Obj. 8, oc. 4, Hartnack. 



Fig. 4. — Four gill-filaments of Mytilus, seen from the surface of the 

 lamella, and focussed so as to bring the ciliated junctions into view. Obj. 

 4, oc. 4, Hartnack. 



Fig. 5. — Three views at different focus-depths of a bit of a gill-filament 

 of JMytilus. The left-hand figure gives the most superficial view ; the 

 middle, an optical longitudinal section through the narrowest part of the 

 cavity of the filament ; the right-hand figure, such a section through the 

 widest part of the same cavity. The surface epithelium in this last figure 

 should be provided with short cilia. Obj. 8, oc. 4, Hartnack. 



