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 plexus 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 
