SEXUAL CHARACTERS — ELASMOBRANCH FISHES 379 



ADDENDUM 



THE RECTAL GLANDS OF ELASMOBRANCHS 



It is generally believed and commonly taught that the rectal 

 gland of Scyllimn is a mucous gland. A certain text-book makes 

 the statement that it "is accessory to the thyroid." Accord- 

 ingly, in September, 1919, I sectioned the rectal gland of Scyl- 



Fig. 14 R,hina squatina. Transverse section of the labial organ. Alum- 

 cochineal. 7n.s.c., mucus-secreting cells. 



lium with the result that neither assumption appears to be cor- 

 rect (fig. 15). 



The muscular coat surrounding the gland is feebly developed 

 and the whole organ is poorly supplied with blood-vessels — a 

 remarkable circumstance in view of the fact that the gland 

 receives apparently the whole supply of the posterior mesenteric 

 artery. 



The glandular portion of the organ consists of a number of 

 convoluted tubules, which, except at their entrance to the 



