GILLS 



403 



lamella, united with one another along the anterior, ventral, 

 and posterior edges of the gill, but free dorsally. The gill 

 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. /), which 

 extend between the two lamellae and divide the intervening 



IV.t 



FIG. 102. Diagram of the structure of the gill of Anodotita. 



The gill is made up of V-shaped gill-filaments (f) arranged in longitudinal series 

 and bound together by horizontal inter-filamentar junctions (i.f.j) which cross 

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

 (as) leading from the outside and opening (0s') into the cavity of the gill. The 

 latter is divided by vertical partitions, the inter-lamellar junctions (/. l,j\ into 

 compartments or water-tubes (?>. t\ which open also into the supra-branchial 

 chamber ; b. v. blood-vessels. (From Parker and Haswell's 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 gill is due to 

 the fact that each lamella is made up of a number of close-set 

 gill-filaments (Fig. I02,/): 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 gill the filaments of the two lamellae 



D D 2 



