No. 415.] NEREIS VIRENS SARS. 571 
direct nervous connection with the hind end, although a well- 
formed nerve cord was present in the tail itself, This condi- 
tion of the nervous system thus closely resembles that which 
we have here described in Nereis. 
Andrews thinks that the balance of evidence favors the 
conclusion that these cases of bifurcation may be produced 
in the adult by traumatic interference ; all the conditions may 
be thus explained, and some can be accounted for in no other 
way. But though he performed many regeneration experi- 
ments on both earthworms and Podarke, no duplications were 
produced. This, however, he does not consider astonishing, 
as examples of bifurcation are extremely rare under natural 
conditions, although loss of parts followed by regeneration is 
constantly taking place. 
Andrews accounts for the independent condition of the 
nerve cords in the bifurcated specimens of Podarke by assuming 
that the short isolated part represents a piece formerly con- 
nected with the main nerve cord, which has failed to reunite 
with it. To quote his own words: “We naturally suppose 
here that a wound has healed over in such a fashion that the 
old nerve cord does not reunite, but that the distal end remains 
as an isolated stump, while the proximal end grows down into 
the new terminal that is formed, abnormally, in place of the 
injured tissue, or at the place of injury to the tissue of the 
normal terminal." 
The conditions which we have described in the interpolated 
nerve cord of Nereis do not allow the application of Andrews's 
assumption. The abnormal nerve chain does not extend into 
the normal somites anteriorly, but is wholly restricted to the 
interpolated region, and must therefore have been formed after 
the assumed injury to the worm ; then, too, its finer structure 
-differs from that of the main nerve cord, more especially at the 
anterior end, where we should expect to find it most closely 
resembling the normal cord if it represented a detached portion 
of it. In this Nereis, therefore, the interpolated nerve cord 
undoubtedly developed as an independent structure. 
It is well known that in nearly all annelids the cells of each 
metamere behind the head region possess the latent power 
