55 



large "lateral cells" (I.e. fig, 40), bearing long dense 

 cilia. External to these are small non-ciliated f^land 



cells, and at the angles, the small, flattened "latere - 



a c ! : 

 frontal'' cells (l.f.c. fig. 40), with a single rov; of stiff 



cilia. The outer edge of the lamina ia occupied by numer- 

 ous small "frontal-cells** (f. c. ) v/hich bear numerous, weak- 

 er cilia. The two broad sides of the lamina are composed 

 of very flat cells without cell outlines or regular ar- 

 rangement, and are connected together by niimerous connect- 

 ive tissue cells which penetrate the blood space of the 

 lamina (b.S. figs. 38,40). In their minute structure 

 (fig. 41) the anterior ton filaments arc essentially like 

 the rest of the gill, except that the "frontal cells" are 

 more numerous, and the middle ones bear no cilia. The 

 first filament is only a half filament, indicating that 

 the filaments are formed by perforations in a gill mem- 

 brane, and not by the latter precocious fusion of gill 

 filaments. The long epibranchial canal is sparsely cil- 

 iated, and it seems that the function of the anterior ten 

 filaments is to get rid of superfluous water in the ante- 

 rior end of the burrow. 



