THE PRINCIPLES OF EMBRYOLOGY 477 
it not a gland which secretes into a duct and might therefore be 
expected to be innervated in the same way as other secretory glands ? 
Although there is a strong primd 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, Retzius 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 
ccelomostomes, 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, 7.¢. true nephridia. 
As to the lining epithelium of the peritoneal, pleural, and 
pericardial cavities—i.c. 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, ete., 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 
