THE PRINCIPLES OF EMBRYOLOGY 477 



it not a "land which secretes into a duct and rnight therefore be 

 expected to be innervated in the same way as other secretory glands ? 

 Although there is a strong prima facie presumption in favour of 

 the existence of renal secretory nerves, yet according to the universal 

 opinion of physiologists no evidence in favour of such nerves has 

 hitherto been found ; all the phenomena of excretion of urine 

 consequent on nerve stimulation are explicable by the action of 

 nerves on the renal vessels, not on the renal cells. Not only is the 

 physiological evidence negative up to the present time, but also, I 

 think, the histological. On the one hand, Eetzius has failed to find 

 nerve-connections with kidney-cells ; on the other, Berkley has 

 obtained such evidence with the Golgi method, but failed entirely 

 with methylene blue. I do not myself think that the evidence of 

 the Golgi method alone is sufficient without corroboration by other 

 methods, and, in any case, Berkley's evidence does not show the 

 nerve-fibres terminating in the kidney-cells, in the same way as can 

 be shown by modern methods to exist in the case of epithelial cells 

 of the surface, etc. Quite recently another paper on this subject has 

 appeared by Smirnow, who appears to have obtained better results 

 than those given by Berkley. 



Apart from these physiological and histological considerations, 

 this question is also dependent upon the nature of the development 

 of the excretory organs, for, according to Lankester, all excretory 

 organs may be divided into the two classes of nephridial organs and 

 crelomostomes, of which the former are largely derived from epiblast. 

 We should, therefore, expect to find secretory nerves to nephridial 

 organs, though possibly not to ccelomostomes. The kidneys of the 

 Mammalia are supposed to be true ccelomostones, although, according 

 to Goodrich's researches, the excretory organs in Amphioxus are 

 solenocytes, i.e. true nephridia. 



As to the lining epithelium of the peritoneal, pleural, and 

 pericardial cavities — i.e. the mesothelium — there is no definite 

 evidence that these cells are provided with nerves. Such surfaces 

 are remarkably insensitive in the healthy condition, and the pain 

 in such cavities is essentially a pressure phenomenon and referable 

 to special sense-organs, such as Pacinian bodies, etc., rather than 

 to the mesothelium itself. 



These sense-organs are identical in structure with those in the 

 skin, and, as Anderson has shown, the nerves of these organs 



