';2 



ly, a pair of lar^e pallial nerves (p.n. Vir,3, 33-. .5, GO) 

 passes backwards to innervate the posterior part of the 

 mantle, including the siphons and the muscles of the pal- 

 ettes. The branchial nerves (b.u.) pass laterally, close- 

 ly associated with the osphradiiom, and then innervate the 

 sills. 



This description of tlie nervous system differs es- 

 sentially from that of Quatrefages (15) which has hereto- 

 fore been accepted. He thought the tvio cerebral ganglia 

 closely fused and the pedal rudimentary and separate. I 

 have no doubt that he mistook the pedal ganglia for the 

 cerebrals; his figures shov; this. But v/hat he observed 

 and figured as the two very small pedal ganglia I do not 

 know. It has been seen that while they are not so large 

 as in forms v/ith a large foot, they are not at all rudi- 

 mentary. 



Otolith. - The larva leads an active locomotor life, and 

 some means for distinguishing the position of its posses- 

 ser is very essential. But the adult "Ship-worm" may as- 

 svime any position, and the otoliths become useless and de- 

 generate. After attachment, they soon cease to grow, -^-^^ 



