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, which is enlarged into a well-marked sub-oesophageal 
ganglion lying in the epidermis. ‘This hes 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 : 
(1.) The Eecardines, whose shell is chitinous and but slightly 
strengthened by 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 
1S NO ANUS. 
Argiope, Terebratula, Terebratulina, Rhynchonella, 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 les uppermost. 
In some genera, as Argiope and Lingula, the body 
occupies most of the space enclosed by the valves of the shell ; 
in Zerebratula 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 
