SEXUAL CHARACTERS ELASMOBRANCH FISHES 



369 



border somewhat resembling columnar cells, with nuclei not 

 quite so elongated; no doubt they are a modification of the 

 spindle-shaped cells, and suggest by their appearance that they 

 may secrete mucus, without being actually what are termed 

 mucus-secreting cells in Galeus. No evidences of mucus are 

 discernible, neither in the cells themselves nor in the lumen of 

 the duct. 



c.t. 



Fig. 7 Lamna cornubica, transverse section of siphon and gland, l.m., longi- 

 tudinal muscle; cm., circular muscles; c.t., connective tissue; Gl., gland; L., 

 lumen. 



A recent theory in human physiology may receive some cor- 

 roboration from the investigation of the clasper glands. The 

 fundamental principle is that there are no such nerves as vaso- 

 dilators, but that inhibition of the plain muscle of arterioles is 

 really produced by the agency of a chemical by-product, or 

 metabolite, originated either in the neighboring muscle or a 

 neighboring gland. 



The large amount of erectile tissue in the penis, and its obvious 

 control by the erigens nerve, whereas there is comparatively 



