XXVlll INTRODUCTION. 



Generally there is extreme difficulty in making out the 

 details of the system in the marine forms. In Membrani- 

 pora membranacea Nitsche has only detected mere rudi- 

 ments of nerve-trunks, on the surface of the ganglion. 

 Ehlcrs has done the same in HypojjhoreUa. In Loxo- 

 soma Salensky has traced various filaments to the tactile 

 organs on the sides of the body"^ ; whilst Nitsche has 

 described three nerve-trunks as given off on the op- 

 posite sides of the ganglion in Pedicell'ma, which soon 

 divide and supply the tentacles (Woodcut, fig. xi,). 

 Two of smaller size were also observed passing from the 



Fig. xi. 



■nU-y^ 



Ganglion or Nervous centre, 

 nt. Nerve-trunks, gc. Ganglionic cells. 



anal surface towards the reproductive organs. The gan- 

 glion itself consists of a solid membranous envelope, 

 inclosing a mass in the outer region of which no struc- 

 ture is distinguishable, but which is made up towards 

 the centre of large cells with granular contents and a 

 nucleusf. 



* " Etudes sur les Bryozoaires Entoproctes," Ann. d. Sc. Nat. 6" ser. Zool. 

 Tol. V. (1877), Article no. -3, pis. xii.-xv. 



t Nitsche, " Ueber die Anatomic von Pcdkcllina echinafa," Sars, Zeitsch. 

 i. wissenseli. Zoul. xx. Heft 1, p. 28. 



