16 SCIENCE PROGRESS. 
nection with the reduction in size and enclosure of the 
chambered shell), higher forms show a series of stages in 
its subsequent degradation, until it is finally lost in the 
Octopoda. The absence of a pallial commissure in Vautzlus 
also supports Pelseneer’s view that in Cephalopoda this 
structure is not of any primary importance. 
At the same time when Pelseneer added a paragraph to 
the effect that the supra-rectal commissure of the Amphi- 
neura is also a merely secondary junction of the pallial 
nerves, he was probably not yet acquainted with Haller’s 
work on Lo¢éza, and allowed his views upon the Polycheete 
ancestry of the Mollusca to bias his interpretation of the 
Molluscan nervous system. 
In a recent paper on the anatomy of Mautz/us Mr. 
Graham Kerr (13) also refers to the question of the supra- 
rectal commissure. It will be remembered that in Mazdéz/as 
the pleuro-visceral ganglia of the two sides form a stout 
ganglionic band encircling the cesophagus in the region of 
the cerebral ganglia. The pallial nerves radiate from the 
lateral portions of this half-ring, and the pair of viscera 
nerves arise from the ventral portion. The visceral cords 
pass backwards on either side of the vena cava, and, after 
giving off the branchial nerves, are prolonged posteriorly as 
far as the post-anal papilla, behind which Mr. Kerr has 
recognised an apparent anastomosis. Mr. Kerr adds that 
in this case “the homologue of the pleuro-visceral cord of 
Chiton is not merely the posterior sub-cesophageal nerve- 
mass, but rather the two lateral portions of this, together 
with the post-branchial prolongations which run on either 
side of the vena cava. The mesial part of the posterior 
sub-cesophageal nerve-mass would therefore be a secondary 
fusion between the nerve-masses of the two opposite 
sides.” 
In his suggested homology of this possible post-anal 
(z.e., supra-rectal) commissure of the visceral nerves in 
Nautilus with the supra-rectal “commissure” of Chzton, 
