304 



J. H. ORTON. 



described in this Journal (1, pp. 448, 455). I thouglit formerly that this 

 mucus was secreted by the epithelium of the gill-filaments (loc . cit . ) , but there 

 is no doubt now that the greater part is secreted by the glandular cells at 

 the base of the filaments, although it is not unlikely that a certain amount 



l.c. 



Fig. 12.* — Transverse section of the endostyle of Crepidula (x about 105). 



EN. 



g-f- 

 f.c. 

 l.c. 



g.s. 

 c.gr. 



I.ch. 

 E.ch. 



Arrow indicating the direction in which the mucus from the endostyle is 

 passed on to the base of the gill-filaments. 



Two rows of groups of gland cells in the endostyle, between and to the left 

 of which is a group of ciliated cells with apical nuclei. 



Gill-filament. 



Frontal epithelium and frontal cilia on gill-filament. 



Lateral cilia on gill-filament. 



Gill-fi-lament support. 



Ciliated groove to the left side of the endostyle. 



Epithelium of mantle the cilia on which lash towards the main food- 

 channel on the right side of the body as indicated by the arrow 

 placed alongside. 

 Inhalent chamber. 



Enhalent chamber into which the main current is passed from the 

 inhalent chamber as indicated by the arrow crossing the gill- 

 filament. 



of mucus may be secreted by the epithelium of the gill-filaments. These 

 groups of grandular cells may be properly termed an endostyle, since they 



* I am indebted to Mrs. Orton for the drawing for this figure as well as those for 

 figures 1, 2, and 8, and also for assistance with all the other drawings except that for 

 Fig. 3 ; and also to Mr. E. Ford for kindly lettering Figs. 3, 4, 6, 7, 9 to 12. 



