53 



ly where the gills oJ" the two sides diverge from each oth- 

 er. As the ^anterior ten Tilatnents become separated i'rom 

 the rest of the gill, the epibranchial cavity remains as a 

 long, very narrow canal (op, ca. figs. 28-31) which lies 

 in '.he mantle on either side external to the afferent 

 branchial vein, and adjacent to tlie groove described be- 

 low. 



The tv/o limbs of a gill lamina (fig. 37) form almost 

 a ri':;ht anrle v;ith each other. At the angle thore is a 

 ciliated groove (figs. 32,34, 37) v/hich expands the full 

 length of the gill in young specimens (fig. 6), and in ad- 

 ults, in addition, connects the anterior ten filaments 

 v/ith the rest of the gill (figs. 9,28-31). In the adult, 

 the connecting part of the groove, then, is really a part 

 of the gill and is homologous with the groove of one fil- 

 ament in other parts of the gill. The minute structure of 

 the groove is as follows:- Tlie lining cells are in the 

 main strongly ciliated and colvimnar (fig. 44) , but there are 

 distributed among them nvimerous mucous gland cells. The 

 internal surface of the mantle opposite the edge of the 

 gill, also forms a groove lined by strongly ciliated cells 

 with gland cells among them, and this with the groove of 

 the gill forms a sort of tube which conveys food to the 



