The anatomy of Lottia gigantea Gray. 47 



nerves usually leave the palliai nerves just as they pass under the 

 circumpallial sinus, before joining the ring nerve. They pass upward 

 over the sinus and branch out under the epithelium of the dorsal sur- 

 face of the pallium, branches passing both inward and outward (M. N'). 

 They lie above the main marginal system. 



There is still another set of nerves in the mantle, which are very 

 difficult to demonstrate, and can be seen only in particularly favorable 

 specimens. It so happens sometimes that in specimens macerating in 

 weak nitric acid, a stage arrives where all the muscular and con- 

 nective tissue becomes semi-transparent or translucent, but the nerves 

 are not aft'ected at all and remain opaque and whitish. If one secures 

 such a favorable specimen he will be able to see these nerves under 

 bright sunlight. They are exceedingly fine and branch over the floor 

 of the sinus and arterial spaces of the mantle in such a way that if 

 the dorsal sheet of muscle is stripped off the mantle, no further dis- 

 section is necessary to show them {M. N"). They are apparently given 

 otf from the circumpallial, or some of its branches, because they are 

 more prominent in the region of this nerve, and fade out toward the 

 inner edge of the mantle. No direct connection with the circum- 

 pallial could be demonstrated, because so soon as one would try to 

 lift it up, the very delicate connections would be broken, if they really 

 existed. From the nature of the anastomosing I have no hesitation 

 in saying that these are nerves. They have been drawn in for only 

 a small portion of the mantle, in the figure, but were seen on the 

 opposite side, in front, and in the rear. 



The pleuro-osphradial connective. A rather remarkable 

 nerve (P.O.C) is that which joins the left pleural ganglion with 

 the osphradial nerve. I have been able to demonstrate this only on 

 the left side of the body. This connective issues from the left pleural 

 between the two palliai nerves, and pursues a course to the spindle 

 muscle close beside the left anterior palliai. Soon it enters the 

 muscular tissue and turns abruptly upward, piercing the thick muscles 

 forming the floor of the anterior angle of the pericardium. Just 

 below the surface, however, it is joined by the osphradial nerve, and 

 at the junction the osphradial nerve turns forward as the ctenidial 

 nerve (Ct.N). Usually, but not always, the left posterior parietal 

 nerve leaves at this point also, and passes back to join, as already 

 pointed out, the posterior palliai. Consequently on the left side the 

 osphradial nerve is connected with the palliai nerves in two different 



