25 
It is not here for the first time that a close aflinity between 
the nervesystem of Mollusks and Plathelminths is hinted at. O. and 
R. HERTWIG in their last paper (8, p. 113) have defended the same 
thesis with different arguments and have combated the more gener- 
ally current idea that Annelids and Brachiopods were in some way 
celosely allied to the Mollusks. It appears to me that Proneo- 
menia makes their reasoning all the more acceptable and might 
serve to strengthen the foundation upon which they have laid down 
their classification and divided the Bilateria into the two subdivi- 
sions of the Enterocoelia and the Pseudocoelia, in case it may prove 
possible to overcome the very serious objections against this 
distinetion which BALrour (1, vol. Il. p. 297) has lately pointed out. 
Finally I must notice that the presence of the latero-pedal com- 
missures, even in the posterior extremity of the animal, together 
with the fact of the pedal nerves being united in that region by 
a strong commissure below the rectum may perhaps serve to 
remove the diffieulty which SpexeeL has encountered in his ex- 
planation of the nervous system of Chiton, without it being requi- 
site to appeal to a displacement of the anus. The two longitudinal 
stems being originally so strongly connected along their whole 
length, it appears to be of secondary importance whether (in those 
groups which here depart from the parent stock and diverge in 
different directions) the infero-reetal commissure, together with 
one of the last latero-pedal commissures gain in importance, the 
pedal nerves simultaneously shortening and losing their connec- 
tion with this commissure and also their anterior latero-pedal com- 
missures (primitive Prosobranchs?), or whether the superorectal 
commissure predominates with posterior coalescence of the longi- 
tudinal stems and loss of the pedal commissures (Chaetoderma) or 
with retention of the pedal commissures (Neomenia) or finally 
with loss of all conneetion whatever between the posterior supero- 
rectal commissure and the pedal nerves (Chiton). 
This suggestion does not pretend to be the result of a careful 
enqguiry into the comparative morphological importance of the dif- 
ferent faets here noticed: it is no more than a provisional sugges- 
