26 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
Caudina likewise I have found that each canal accompanies the 
radial nerve as far as the point at which the latter joins the nerve 
ring ; here it ends blindly. 
Teuscher and Semon maintain, on the contrary, that the hyponeural 
canal is in connection anteriorly with a circular canal which lies on 
the opposite side of the neural band. In the figure of the circular 
canal given by Teuscher (Taf. 22, fig. 6) it lies on the axial and 
anterior side of the nerve ring. Thus it is clear that these inves¬ 
tigators regarded the hyponeural canal as being connected with the 
anterior part of what we now know to be the radial epineural canal 
and the epineural ring canal. 
The anatomical studies of Ludwig und Barthels (’91) on the 
Synaptidae having shown that radial ambulacral canals are wholly 
lacking in this family, we must regard Hamann’s radial Wasser- 
gefcisse in Synapta as hyponeural canals. Each of these has been 
traced forward by Hamann, as will be remembered, to a small and 
short canal which ends blindly behind the nerve ring and which, 
according to his description, is in connection with the tentacles. It 
seems probable, in view of the researches of Ludwig und Barthels, 
that he has erred in regarding this canal as connected with the 
tentacular canals, and that the conditions in the Synaptidae are in 
this particular not unlike those in the Cucumariidae and Molpa- 
diidae. 
Epineural canals .—The epineural canal described and figured 
by most observers who have studied the nervous system in holo- 
thurians, has been regarded quite generally as the result of an 
artificial separation of the external face of the radial nerve 
from the connective-tissue layer of the body-wall. Greeff (’72) 
and TI6rouard (’89) are, so far as I know, the only investigators 
who have stated decidedly that the radial epineural spaces in the 
adult are not the result of artificial breaks between nervous and 
connective tissue, but normal cavities. 
I am of the opinion, that the epineural canals in Caudina are 
normal structures, containing in the living animal a fluid similar 
to that in the body-cavity. It may be thought, that the fibers 
which arise from the nuclei of the covering epithelium of the 
anterior part of the radial‘nerve and pass across the epineural 
space into the adjacent connective tissue are evidence of an arti¬ 
ficial separation of the tissues. The uniformity in the appearance 
of the wide epineural spaces in specimens fixed when the walls of 
