THE LAMELLIBRANCHIA 227; 
individual filament—and consequently the two lamellae of each gill- 
plate—are joined together by bridges or interlamellar junctions, 
which are formed of connective tissue only in the Pectinidae, but 
are vascular in the Aviculidae. Finally, the different elements of 
the branchial apparatus are much more intimately connected in the 
various groups of Eulamellibranchs, in which there are always 
vascular interfilamentar and interlamellar junctions (Fig. 237). 
Thus the blood brought to the gill by the afferent vessel is conducted 
by vessels which run between the lamellae and communicate with 
Fic. 207. 
Adaenarca nitens, Pels., transverse section. br, right internal gill-plate ; 67’, left internal 
gill-plate (without reflected lamina): br’, external gill-plates (with reflected lamina); ca.b, 
byssus cavity ; com.v, visceral commissure ; hep, liver; i, intestine; pa, mantle ; per, peri- 
cardium ; 7, kidney ; st, stomach ; tes, testis. 
the filaments on either hand, forming in this manner the inter- 
lamellar junctions. 
Each gill-plate may be thrown into a very regular series of 
transverse folds, each fold involving a fixed number of filaments ; 
this is the case in the Pectinacea, the Ostraeacea, and the more 
specialised forms of Eulamellibranchia. In the last-named the 
folding is still but slightly marked in the Veneridae, but becomes 
much more so in the Cardiacea (in Tvridacna a single fold may 
contain as many as seventy filaments), the Myacea, etc. In the 
Pectinacea and Ostraeacea the filament forming the junction between 
two successive folds becomes thicker and more important than the 
