696 



THE ANIMAL KINGDOM. 



which are implanted fine close-set chitinoid setae, rarely wanting as in 

 Argiope and Thecidium. They are developed from tubular imaginations 

 of the ectoderm as are the setae of Chaetopoda. Calcareous spicules or 

 plates are often found at the bases of the ectoderm cells, e. g. in Lingula 

 pyramidata and many Testicardines, sometimes in great numbers 1 . The 

 body-walls are supported by a cartilaginoid connective tissue which 

 varies somewhat in character in different Brachiopoda, and in different 

 parts of the same Brachiopod. It may be structureless, and hyaline, or 

 penetrated by cells which often form a reticulum, or be fibrillated. The 

 coelomic aspect of this supporting substance is covered by a unilaminar 

 epithelium which appears to be ciliated wholly, or in places, thus keeping 

 the contained fluid or blood in motion. There are special muscles for 

 opening as well as closing the valves, differing in arrangement in Ecardincs 

 and Testicardines. The muscles are composed of a number of separate 

 parallel fibres each of which has a nucleus and a small remnant of proto- 

 plasm, and the fibres of the posterior occlusor muscles of the shell are 

 transversely striated in some Testicardines. They are attached to the 

 dorsal valve on thickenings of the supporting connective tissue ; to the 

 ventral valve by tendons which appear to be composed of the same 

 substance. The points of attachments cause distinct impressions. The 

 substance of the muscles is said to be reddish. Fine muscular cells occupy 

 in parf the cavity of each cirrus, organs which can be rolled up or 

 extended. The fibres at the edges of the mantle, and those which, occupy 

 the centre of the peduncle when short and solid, as in Testicardines and 

 Discina among Ecardines, or surround its central cavity when long and 

 hollow, as in Lingida, are of a nature doubtfully muscular. They form, 

 however, at the base of the peduncle distinct bundles (adjuster muscles of 

 Hancock) which are inserted on the valves of the shell where they cause 

 impressions. 



The central nervous system consists of a peri-oesophageal ring of some 

 size, its ventral part usually lying posterior to the cirri, its dorsal an- 

 terior to the lip. In Lingula pyramidata this ring contains five ganglionic 

 enlargements, two dorso-lateral, or supra-oesophageal, two ventro-lateral, 

 and a median ventral, or sub-oesophageal. The ganglia lie immediately 

 beneath the ectoderm, which here consists of one or more layers of cells 

 supported on their inner aspect by connective tissue. The ring of Crania 

 is said to contain one dorsal, or supra-oesophageal, ganglion, and two sub- 

 oesophageal. As to the Testicardines , Hancock has described in Wald- 

 heimia aus trails a ring similarly constituted to that of Lingula (supra}, but 

 van Bemmelen finds only a single supra- and a single sub-oesophageal 

 ganglion connected by a commissure. So too in Argiope Kowalewskii 

 according to Shipley, wKereas Schulgin found in the same animal three 



1 They do not occur in Lingula anatina, .L. affinis, Waldheimia or Khynchonella. 



