OBSERVATIONS ON POLYZOA. 109 



er it is one single trunk on the dorsal end. There is, in 

 fact hardly any difference between the nerve masses of Plu- 

 matella and Pectinatella, taking any two individuals at 

 random, one from each genus, which may not be equaled 

 by selecting two zooids from a single colony in any species. 

 Although there are sometimes considerable differences be- 

 tween individuals of Pectiuatella magnifica and those of 

 Pluinatella, I have yet to see a greater difference than 

 may be found between difierent zooids of the same species. 



The same contractions and hoistings of the mass are 

 as frequent in all the remaining genera of the suborder 

 as in Fredericlla, the contraction invariably happening in 

 the same manner and towards the posterior side, or side 

 corresponding to the ventral side of the mass in Frederi- 

 cella (PI. 11, fig. 3). The nerves of the alimentary canal 

 were not observed in any other genus than the last named, 

 but it is probable, that in propitious lights they may be 

 found somewhere on the anterior side between the lopho- 

 phoric and epistomic nerve-trunks. The polypidal nerve- 

 trunks of all the Hypocrepiaiv genera are marked by the 

 presence of one additional pair of nerve-branches, the 

 Brachialr-banches. These part from the polypidal nerves 

 and striking out laterally enter the endocyst either on the 

 side, or close to the bases of the arms and undoubtedly 

 supply them with nervous filaments (PI. 11, fig. 1, T"). 



The conditions of the brachial branches of the lopho- 

 phoric nerve, are considerably altered in Plumatella, and 

 its allies, to correspond with the extension of the arms 

 and the larger number of tentacles to which they distribute 

 filaments. Their length therefore is much greater, but 

 otherwise they do not appear to have changed (Pi. 13, fig. 

 13, U). Prof. Allman supposes that the oral and bra- 

 chial branches from the opposite sides of the lophophore 

 join each other on the median line, thus forming a nervous 

 collar about the mouth. I have, however, entirely failed 

 both in Fredericella (PI. 9, fig. 1), and in Cristatella 

 .(PI. 13, fig. 13), to substantiate this opinion, Dumor- 

 tier and Van Beneden figure nerves in the so called Alcy- 



