BRACHIOPODA. 697 



sub-oesophageal ganglia, i. e. two ventro-lateral and a median. All the 

 ganglia are in continuity with the ectoderm in Argiope (Shipley), but van 

 Bemmelen found this to be the case only with the sub-oesophageal. 

 Ganglion cells occur in the commissures, as well as in the nerves to the 

 lophophore, or arms. Three nerves pass, according to van Bemmelen, along 

 each arm, one from both the supra- and sub-oesophageal ganglion, the third 

 from the commissure, and are connected, especially that from the supra- 

 oesophageal ganglion, with a rich ganglionic plexus. The sub-oesophageal 

 ganglion gives off nerves to both the dorsal and ventral mantle-folds, in 

 which they branch as they pass towards their free margins, as well as to the 

 muscles and viscera. The disposition of the nerves is similar in Lingula 

 (Beyer). Special sense organs are usually said to be wanting in the adult. 

 Rudimentary eyes are stated by Schulgin, citing Kowalewsky, to be found 

 in Megerlia ' on the inferior,' i. e. posterior ' margin of the tentacular disc not 

 far from the mouth.' In Argiope Kowalewskii two parallel bands of massed 

 ectoderm cells lie, according to Schulgin, posterior to the lophophore not 

 far from the mouth, the one nearest consisting of ' specific/ i. e. sensory 

 cells, innervated from the sub-oesophageal ganglia. The same author states 

 that rod-like bi-nucleate sense-cells, connected basally to a nerve-filament, 

 are found among the pyramidal ectoderm cells of the margins of the 

 mantle. Joubin has traced in Crania filaments from the brachial nerve 

 plexus to pads of elongated ectodermic cells at the bases on the inner 

 aspect, i. e. the one turned to the brachial groove, of each cirrus, and 

 to a continuous band of similar cells on the outer aspect of the same 

 structures. 



The mouth opens into the brachial groove at a spot coinciding with 

 the centre of the convexity of the horseshoe. It leads into an oesophagus 

 which turns anteriorly and dorsally, and then curves back upon itself and 

 passes into the stomach. The latter is enlarged, and receives the ducts of 

 the so-called liver lobes, which vary in number in different Brachiopoda, 

 e. g. two in Argiope, &c., five in Lingula pyramidata. The stomach is 

 followed by the intestine, which turns towards the ventral valve in the 

 T e stic ar dines, and, sooner or later, ends blindly. The Ecardines have an 

 anus. In Lingula pyramidata the intestine skirts along the right side of 

 the body ; but in L. anatina it forms two loops before it does so ; in Dis- 

 cina the curvatures are more complex ; in Crania more simple, consisting 

 of a three-quarter circle to the left, and in both there is a terminal dilated 

 rectum. This rectum in Crania lies in the middle line between the two. 

 posterior adductor muscles, and the anus opens into a sinus between the 

 posterior ends of the two valves, where the hinge and peduncle should be 1 , 

 and not into the pallial cavity between the two valves as in Lingula and 

 Discina, where it lies on the right side but nearer to the ventral valve than 



1 See Joubin, A. Z. Expt. (2), iv. 1886, pp. 218-19, figs. 2, 3, and p. 233. 



