TYPE PEOSOPYGIA. 



271 



however, it opens posteriorly, while in Terebratuliaa, Argiope, 

 and Waldlieimia, in fact in all the Testicardines, it ends 

 blindly, the anus being wanting. 



The nervous system consists of an oesophageal ring lying 

 in the connective tissue substance, the lower portion being in 

 connection with the ectoderm and slightly swollen, represent- 

 ing probably the subcesophageal ganglion of the Annelida ; 



ov 



ue 



am 



pe 



FIG. 120. STRUCTURE OF Terebratulina septentrionalis. 



am = adductor muscle. ne = nephridium. 



i = intestine. ov = ovary. 



I = liver-lobes. pe = peduncle. 



Ip = lophopbore. rm retractor muscle. 

 m = mantle. s = shell. 



a similar swelling in the dorsal portion of the ring represents 

 the suprao3sophageal ganglion, and in addition there are usu- 

 ally two further lateral ganglion-like swellings. Nerves pass 

 off from the upper ganglion to the lophophore and other 

 regions, and from the lower one to the mantle, muscles, etc., 

 both sets terminating in the superficial layers of the lopho- 

 phore-tentacles or of the mantle in a network of ganglion 

 cells and fibres. No trace of a ventral nerve-cord in addition 

 to the suboesophageal ganglion is present. 



Sense-organs are but poorly developed, neither eyes nor 

 auditory organs occurring. The tentacles on the lophophoric 

 arms are in all probability sensory, as indicated by their rich 

 nerve-supply, and the papillae of the mantle-ectoderm which 



