THE STING-RAY. 



437 



cavities, occupied by a mass of homogeneous yellow material 

 staining yellow by Van Giesen's method. These cavities tend 

 throughout the whole series of sections to arrange themselves 

 into two ducts or canals, one lying near the centre of the gland or 

 towards the ridge, and the other lying towards the lateral 

 margin in the direction of the teeth. The follicles seem to 

 empty themselves either into one canal or the other. As each 

 duct or canal becomes filled with secretion it bulges the pigment- 

 layer so as to make it protrude externally. On the peripheral 

 margin of the lateral canal this bulge is surmounted by a curious 

 nipple-shaped projection which appears throughout the whole 

 series of sections, at times distended, at times empty and flattened. 

 Some of the sections show the nipple discharging a fluid from its 



Text- figure 6. 



Trygon pastinaoa. 



A-C. Series of sections progressively diminishing towards tip. 



e.n. Elongated nipple, e.n.l. the same enlarged (note bulbous tip containing 

 secretion). Le. lateral canal, m.c. canal of median ridge (»•.). s/. secreting 

 filaments, s.f.l. the same enlarged. 



tip, and one feels convinced that these sections actually show 

 the secretion from the lateral canal being discharged externally. 

 Towards the tip of the spine, where the groove is smaller, the 

 nipple is prolonged into a filamentous tube. 



By counting the sections in series and observing the presence 

 or absence of a nipple-like projection from the lateral canal, one 

 is able to estimate approximately the size of these projections. 



Proc. Zool. Soc— 1916, No. XXIX. 29 



