THE ANATOMY OF THE BRITISH SPECIES OF 

 THE GENUS SOLEN. Pt. i.i.* 



By H. H. B7.00MER. 

 (Plate ii.) 



Nervous System. 



Solen pnsis, L. (PL ii., figs. i8 — 20. 



The cerebro-pleural ganglia {Figs. 18-19, ^-- P- ^^■) ^''^ situated 

 under the anterior bifurcated parts of the anterior retractor pedis 

 muscles, just in front of the mouth. The two ganglia can be seen in 

 situ through the transparent ventral integument. They lie some 

 distance apart, but are connected by a commissure (Figs. 18 and 19, 

 G. P. C). Anteriorly each ganglion gives rise to an anterior pallial 

 ntx\Q (A. P.N.) running in an anterio-lateral direction, towards the 

 posterior edge of the anterior adductor muscle ; some distance before 

 reaching the latter, a large branch (V. A. N.) leaves the nerve on its 

 inner side, and traverses the whole length of the ventral surface of the 

 muscle close to the lateral edge, innervating it with a number of small 

 branches. About one-third of its course along the muscle it gives off 

 a large branch which passes along the transparent portion of the 

 mantle-lobe. Both nerves eventually join the outer circumpallial 

 nerve (0. C. N.). 



'When the anterior pallial nerve reaches the transparent portion of 

 the mantle-lobe, a large branch leaves it and crosses the mantle in a 

 ventral direction and divides, both portions joining the outer circum- 

 pallial nerve. This latter nerve, shortly after leaving the main pallial 

 nerve is connected with the inner circumpallial nerve (Fig. 18, LC.N.), 

 which proceeds in a posterior direction, and curving ventrally joins 

 the posterior pallial nerve. 



The main anterior pallial nerve (A.P.N.) pursues an anterior 

 direction. From it four large branches originate, all of which pass 

 ventrally and eventually join the outer circumpallial nerve (O.C.N.). 



Each cerebro-pleural ganglion also gives rise to another anterior 

 nerve (Figs. 18 and 19, J).A.N.), which passes along the ventral 

 surface of the anterior bifurcation of the retractor pedis anterior 

 muscle, and then along the dorsal surface of the anterior adductor 

 muscle, on its course giving a number of small branches to both 

 muscles, the liver, and the dorsal integument. The ganglia also give 

 off several small nerves which pass direct to the muscles and viscera 



Posteriorly a connective joins each cerebro-pleural with the 



* See :inte, vol. viii. p. 97. 



