GILLS 



403 



the anterior, ventral and posterior edges of the lamina, 

 but free dorsally. The lamina has thus the form of a 

 long and extremely shallow bag, open above (Figs. 102 

 and 103) : its cavity is subdivided by vertical plates of 

 tissue, the inter-lamellar junctions (i. I. j), which extend 

 between the two lamellae and divide the intervening 



FIG. 102. Diagram of the structure of a piece of gill of Anodonta. 

 The gill-lamina is made up of V-shaped gill-filaments (/) arranged in longitudinal 

 series and bound together by horizontal inter-filamentar junctions (. /. j) which 

 cross them at right angles, "forming a kind of basket-work with apertures, the 

 ostia (os) leading from the outside and opening (os'} into the cavity of the gill. 

 The latter is divided by vertical partitions, the inter-lamellar junctions (. l.f), 

 into compartments or water-tubes (ii\ <), which open also into the supra- 

 branchial chamber ; b. v. blood-vessels. (From Parker and HaswelTs Zoology.) 



space into distinct compartments or water-tubes (Figs. 101 

 and 102, w. /), closed ventrally, but freely open along the 

 dorsal edge of the gill. The vertical striation of the 

 laminae is due to the fact that each lamella is made up of 

 a number of close-set gill-filaments (Fig. 102, /) : the 

 longitudinal striation to the circumstance that these 

 filaments are connected by horizontal bars, the inter- 

 filamentar junctions (i. f. j). At the thin free or ventral 

 edge of the lamina the filaments of the two lamellae are 

 continuous with one another, so that each lamina has 



