176 ZOOLOGY 



The ova are modifications of the cells lining the coelom. 

 There are four ovaries, one on each side in the dorsal and 

 in the ventral shell. The cells are borne on an axis, and all 

 stages from the ripe ovum to the unmodified peritoneal cell 

 may be seen on the same axis. The ripe ova fall into the 

 coelom and leave the body through the nephridia. They 

 undergo the early stages of their developement in the brood 

 pouches. No testes have been described, and it is uncertain 

 whether this species is hermaphrodite or not. 



The nervous system consists of a circum-oesophageal nerve 

 ring, vrhich is enlarged into a weU- marked sub -oesophageal 

 ganglion lying in the epidermis. This lies in that part of the 

 body-wall which overhangs the mouth, just behind the base of 

 the tentacles. The nerve ring swells into a small supra- 

 oesophageal ganglion, which is not so large or so well marked 

 as the sub-oesophageal. The latter gives off a nerve which 

 runs round the edge of the lophophore, and nerves to the 

 dorsal and ventral mantles. 



The Brachiopoda are divided into two orders : 



(i.) The Ecardines, whose shell is chitinous and hut slightly 

 strengthened hy a deposit of calcareous spicules. The shell has no 

 hinge and no internal skeleton to support the arms. The ali- 

 mentary canal terminates in an anus, median and ventral in 

 Crania and lateral in Lingula. 



Lingula, Glottidia, Crania, and Discina. 



(ii.) The Testicardines have shells composed of calcareous 

 spicules, the valves are hinged together, and there is usually an 

 internal skeleton supporting the arms of the lophophore. There 

 is no anus. 



Argiope, Terebratula, TerebratuUna, EhynchoneUa, Theci- 

 dium, Waldheimia. 



In the Lingulidae the dorsal and ventral valves are about 

 the same size ; in all other Brachiopods the ventral is much 

 the larger, and except in Crania always lies uppermost. 



In some genera, as Argiope and Lingula, the body 

 occupies most of the space enclosed by the valves of the shell ; 

 in Terebratula and some others the body takes up but a small 

 portion of this space, the remainder being occupied by the arms 

 of the lophophore, which stand out from the surface of the 



