422 
H. BURY. 
Balanoglossus the water-pore and the short tube by which it 
communicates with the enterocoel represent a primitive nephri- 
dium. It would seem from Hartog’s observations that in the 
adult the nephridial function is transferred to the water- 
vascular system. 
The existence of a pair of anterior enterocoels in Echinoderms 
is to some extent opposed to the homology which I formerly 
attempted to establish between the anterior enterocoel of An- 
tedon and that of the larva of Balanoglossus. It is true that 
the existence of two pores belonging to the anterior cavity in 
the larva of B. Kupfferi (30) is evidence of the paired nature 
of this cavity ; but, on the other hand, two distinct anterior 
cavities are never, so far as I know, present in Balanoglossus, 
while no instance is yet known in which a pore normally occurs 
in connection with the right anterior enterocoel of Echinoderms. 
The present paper, therefore, adduces no new evidence in favour 
of the phylogenetic connection of the Echinodermata and 
Enteropneusta, though it does not seriously weaken the proba- 
bility of such a connection. 
II. Further Development of Hydroccel : Water-Tube. 
Ophiurids. — We left the hydroccel of this group as a 
closed elongated vesicle stretching forwards for some distance 
under the anterior enterocoel, and backwards as far as the 
posterior enterocoel. The next change consists in the forma- 
tion of five lobes on its outer (left) border. This has been 
already described by previous observers, and need not be dwelt 
upon here ; it is only necessary to add that the water-pore 
usually lies at first nearly at the level of the third lobe, but by 
a further shifting forwards of the hydroccel it afterwards 
comes to lie over the interval between the fourth and fifth, or 
even over the fifth (posterior) lobe itself. When this stage 
has been reached we notice the first formation of the water- 
tube (= stone-canal), which arises as an outgrowth of the 
posterior end of the hydrocoel, between the fourth and fifth 
pouches, and has, like the rest of the hydrocoel, a columnar 
