NOTES ON COMMON SPECIES OF TROCHUS. 465 



to oue another, tliey must act as cushions to keep the leaflets 

 from packing" together, the thickened chitinous plates already 

 mentioned contributing to stiffen the leaflet. 



The surface of the leaflet is thrown into folds, which run 

 fairly parallel with the line where the leaflet unites with the 

 gill axis. The epithelium of this part of the gill varies very 

 much in appearance according to the exact direction in Avhich 

 it happens to be cut, but it is not nearly so high as that 

 along the efferent border. 



The afferent border of the leaflet is the one which is most 

 directly exposed in the branchial cavity. Along this edge 

 the epithelium is fairly high and regular, and includes 

 mucus-secreting cells; we do not think it is ciliated (fig. 6). 

 There are no supporting chitinous plates and no cushions 

 near this border; if the topographically lower efferent edges 

 of the leaflets are stiffened and held apart that suffices to 

 keep the leaflets from packing against one another. The 

 mucus-secreting cells of the afferent border must help to 

 keep the leaflet from injury due to rough fragments rubbing 

 against this exposed part. In Trochus, but not in Haliotis, 

 we find the afferent border somewhat expanded (fig. 6), and 

 this may be a cushion arrangement, so the statement above 

 made perhaps needs modification. The appearance of odd 

 fragments in the mucus outside the expanded border sug'gests 

 that the swelling may have the added value of hindering 

 the entry of these fragments into the chinks between the 

 leaflets. 



Notes on the Kidneys. 



The kidneys of Trochus were described by Perrier (8) and 

 Haller (4), and Thiele (12) added the observation of a 

 "nephridial gland" along the left side of the left kidney. 

 Eandles (10) and Pelseneer (7) have both described the peri- 

 cardial communications of the kidneys, and Randies has added 

 correct sketches of the cells typical of the right kidney. We 



