NOTES ON ECHINODERM MORPHOLOGY. 145 
while we both regard the ventral end of this water-tube as 
represented in Spatangus by the incomplete sinuous canal 
(C’ of Koehler’s figures) which lies along the gullet and starts 
from the water-vascular ring (auctorum). 
Koehler attributes no special functional importance to this 
discontinuous water-tube ; whereas I have suggested that its 
two ends may correspond respectively to the water-pores on 
the disc of a Crinoid and the water-tubes by which the water- 
vascular ring communicates with the body cavity. There 
would be a difficulty about this, however, if Koehler is right 
in saying that the tube with columnar epithelium, Teuscher’s 
Steincanal, “ne débouche pas au dehors et ne tarde pas Ase 
perdre au milieu des interstices du tissu conjonctif.””! 
At the beginning of Koehler’s statement of his views which I 
have just quoted, he uses the term “ canal du sable” for an organ 
in Spatangus which he and I both believe to be homologous, 
not with the similarly named vessel in Echinus, but with the 
“ glandular canal” that unites the ovoid gland with the oral 
blood-vascular ring of this type. I rather wonder, therefore, 
at his giving the same name to two vessels which he does not 
consider as homologous. According to his views they have the 
same function, viz. that of effecting the communication between 
the conjoint vascular system and the exterior, the work of the 
glandular canal and water-tube in Echinus being performed 
in Spatangus by the former alone, owing to the incomplete 
development of that part of the system which is homologous 
with the water-tube of Echinus. But would it not have been 
more rational to call the ‘‘ canal du sable” of Spatangus by 
the name of that organ, the glandular canal, to which it is 
unquestionably both homologous and analogous in Echinus? 
As it is, however, Koehler has preferred to use the name 
“canal du sable” for this tube; and most readers would 
therefore regard him as attributing to it the function of admit- 
ting water into the vascular system. This, be it remembered, 
must take place through the organ of excretion, if Koehler’s 
views are the true ones. But, if he will pardon me for saying 
' * Recherches,’ p. 99. 
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