The anatomy of Lottia gigantea Gray. 45 



into smaller branches which pass toward the periphery of the mantle 

 and join the circumpallial nerve (C.P.N). This nerve com- 

 pletely encircles the animal. It lies at a constant distance from the 

 mantle edge, and on the outer border of the circumpallial blood sinus. 

 All the pallial nerves and their branches ultimately reach and join it. 

 A description of the nerve will be deferred till later. Occasionally 

 the tertiary branches of the pallial nerves again divide before reaching 

 the circumpallial. The hinder branch of the anterior pallial (right), 

 after entering the spindle muscle, turns sharply backward and pursuing 

 this general direction divides into two branches which join the circum- 

 pallial at about the middle of the animal. While still within 

 the muscle this posterior branch of the right anterior 

 pallial is joined by a slender nerve (B.Par) given off by 

 the right osphradial nerve. I have called it for convenience 

 of description the right posterior parietal nerve. That of the left side 

 has very similar connections. The anterior prolongation of the right 

 osphradial (R.Par 1 ) joins, in the mantle, the right anterior pallial 

 nerve. Consequently the osphradial nerve may be considered to divide 

 into two terminal branches, both of which unite with the pallials. 

 This is true of the left side also, as will be seen later. 



The right posterior pallial passes directly backward conforming 

 somewhat to the trend of the spindle muscle, which it soon enters 

 and follows nearly to the hind end of the animal, giving off enroute 

 three main branches, which reach the circumpallial after again dividing. 

 As it nears the hind end of the animal the posterior pallial (right), 

 now very much attenuated, passes out onto the mantle and near the 

 median line turns abruptly toward the circumpallial which it joins. 

 A very much slenderer nerve, in fact quite the smallest in that vici- 

 nity (P.P.N"), leaves the posterior pallial just as it turns to join the 

 circumpallial and running a short distance parallel with the last, joins 

 the attenuate, final branch of the left posterior pallial. Thus the 

 ends of the two posterior pallials are joined by a short, fine nerve, 

 which completes an inner ring as it were. It does not need but a 

 glance however to show that this inner ring does not at all resemble 

 Haller's 1 ) "Mantelrandnerv" which is figured as of the same calibre 

 throughout, and with scattered ganglion cells, which the posterior 

 pallials do not possess. 



As on the right side, there are two main pallial nerves issuing 



1) Hallee, 1. c, fig. 1. 



