110 HYATT, 



onella fungosa,* which encircle the oesophagus, and seem 

 to correspond in respect to location with the oesophagal 

 nerve-branches of Fredericella. 



Dumortier was the first to discover the nervous system 

 arid did his work more thoroughly than any succeeding 

 investigator. He demonstrated the existence of two lat- 

 eral ganglia in the nerve-mass of Lophopus crystallinus, 

 and, although I have been unable to see these ganglia with 

 the same distinctness with which they are represented in 

 Dumortier's figures, I have been able to verify his obser- 

 vations in great measure by collateral evidence. 



That there are two ganglia united by a commissure in 

 all the Hypocrepia can hardly be doubtful . The equality 

 in the number of the nerves on each side and their distri- 

 bution, not irregularly from any portion of the mass, but 

 from the two swollen lateral ends, show that these are two 

 ganglionic centres. In Fredericella, however, the com- 

 missure appears to be wanting and further observations are 

 necessary in order to prove that the nerve trunks are inva- 

 riably derived from the sides of the mass. If this is the 

 case, as it appears to be in Fredericella regina, we shall 

 be obliged to regard the nerve-mass of this genus as com- 

 posed of two large ganglia, united by a branchless commis- 

 sure as large, if not larger, than the ganglia themselves. 

 The size of the commissure, however, seems to be imma- 

 terial since I have frequently seen it in Plumatella, Pecti- 

 natella and Cristatella of the same thickness as the ganglia 

 themselves (PL 12, fig. 1, S). It must also be remembered, 

 in comparing the nerve-mass of Plumatella and Frederi- 

 cella, that the depression shown in fig. 12, page 107, is on 

 the side which corresponds to the ventral side of the mass 

 in Fredericella and would be hidden from view in a dorsal 

 view of the mass in the last named genus, even if it ex- 

 isted there. 



Dumortier mentions a peculiarity of Lophopus, which 

 indicates the existence of a colonial nervous system, such as 



*DUMORTIER and VAN BENEDEN. Op. cit. PL 4, fig. 5. 

 fDuMORTiER. Recherche sur les Polypes Comp. de 1'eau douce, Bull, 

 de 1'Acad. Bruxelles, 1835, 2, p. 422. 



