144 



COMPARATIVE ANATOMY 



CHAP. 



anterior jiortion of the intestine reeeives nerves from tlie visceral connectives. Since 

 the fibres of these nerves have been proved to originate in the cerebral ganglia, we 

 may assume that, on the degeneration of the pharyn.v, the buccal connectives united 

 with tlie visceral connectives, so that the intestinal nerves now rise from the latter 

 and do not come direct from the brain. In the Pholadida' and Teredinidcc the 

 visceral connectives are united in front of the i-iscernparietal ganglia by a second 



Fig. 124.— Nervous system of Cardium edule (afler Drost), seen fruni Hie \ ciitral .skle. The 

 left mantle (the right in the figure) has been reniriveil and the right bent back ; tlie foot has been 

 laid on one side. 1, Oral lobes ; 2, 3, 4, pallial nerves, running nearly parallel to the edge ; 2, the 

 nerve of the pallial edge ; d, mantle ; C, gill ; V, point of junction of the principal pallial nerves ; S, 

 jnantle edge of the respiratory aperture ; (», ditto of the anal aperture ; 10, posterior adductor ; 11. 

 viscero-parietal ganglion ; 12, branchial nerve ; 13, foot ; 14, pedal ganglion ; 15, left cerebroxjleural 

 ganglion ; 111, mouth ; 17, right cerebropleural ganglion ; Is, anterior adductor. 



conmiissure, which runs under the intestine, and may perhaps lie considered as a 

 buccal commissure shifted far back. 



The mantle is innervated, as is clear from the above, partly from the cerebro- 

 pleural, and partly from the visceroparietal ganglia. 



The two anterior pallial nerves, which rise from the cerebropleural ganglia, run 

 back along the edges of the mantle, to join the two posterior jiallial nerves which 

 originate in the visceroparietal ganglia. A nerve thus runs jiarallel to the edge of 

 the mantle on each side (nerve of the pallial edge), and like a connective, unites the 

 anterior cerebropleural ganglion with the posterior visceroparietal ganglion. This 



