XI. Brachiopoda 



Perhaps in no group of animals is our knowledge of the general 

 arrangement of the nervous system in such an unsatisfactory con- 

 dition. Various published accounts are not altogether in accord 

 even when the same species is studied. 



Owen, 1835, seems to be the first to detect the nervous system. 

 He describes white filaments which traverse the visceral cavity and 

 end in muscles. 



Huxley, 1854, considers the nervous system to be a ring of 

 nervous tissue about the oral opening. 



Gratiolet, 1857, 1860, describes a considerable mass of gan- 

 glinic material encircling the oesophagus but reduced to a small 

 ring on the upper side of the oesophagus. 



Hancock, 1859, says that the nervous system is easily seen but 

 not clearly defined. In one form studied five centers of nervous 

 tissue were found about the oesophagus, three of which were large 

 enough to be called chief ganglia. He did not find a pallial nerve 

 described by Owen. 



Van Bemmelen, 1883, has a more detailed account of the nerv- 

 ous system. According to this author there is a pair of infra- 

 oesophageal ganglia and two true supra-oesphageal centers. From 

 both, nerves run to the arms. The nerve centers are composed of 

 very small ganglion cells and fibers ; the peripheral nerves are com- 

 posed of straight fibers. 



Beyer, 1886, describes a commissural ring surrounding the 

 oesophagus at its junction with the stomach, in Lingula. There 

 are nerve centers in the ring as follows : one central, two dorso- 

 lateral and two ventro-lateral, these last being the largest. All 

 centers are below the ectoderm and the .nerve cells communicate 

 with the surface. 



Blockmann, 1892-3, gives quite a complete picture of the dis- 

 tribution of the ganglia and chief branches. In his work the lat- 

 eral ganglia are widely separated and little emphasis is given to 

 any supra-oesophageal center. 



Delage and Herouard, 1897, give quite an extensive account of 

 the nervous system. In their general account they speak of a sim- 

 pler nervous system presuming to some extent embryonic condi- 

 tions of connection with the epidermis. There is a large peribuccal 

 collar formed'of two dorsal cerebral ganglia and a ventral ganglion 

 much larger and a little bilobed, with a pair of fine connectives. 

 From the cerebral ganglia nerves go to the arms. From the ex- 

 tremity of the connectives a pair of nerves run to the cirri. Nerves 

 in the arms anastomose and form a nlexus of fibrous cells just under 

 the epidermis. The ventral ganglion gives off, at its posterior 

 angle, a pair of dorsal pallial nerves which run to a corresponding 



