496 RECORD OF SCIENCE FOR 1886. 



Gasteropnds. 



Nervous system of ctenohranchiate gasteropods. — In a memoir upon the 

 nervous system of tlie scuti branchiate gasteropods, Mr. E. L. Bouvier 

 has directed special attention to the character of tlie jiroboscidial com- 

 missure. In a memoir upon the nervous system of the ctenohranchiate 

 gasteropods he had maintained that the proboscidial commissure disap- 

 pears, but that "there is another conuective which is very characteristic. 

 It is that which more oi* less distinctly connects the right commissural 

 ganglion with thesubintestinal. This connective results from the anas- 

 tomosis of the right pallial nerves, which issue from the right commis- 

 sural and from the sub-intestinal ganglia. The author enumerates vari- 

 ous forjns in which this arrangement is found. In the Cerithiidfe the 

 conversion of the anastomosis into a connective may be studied step by 

 step. When once formed it varies very greatly in dimensions. On the 

 left hand side the pallial nerve always retains its origin in the commis- 

 sural ganglion, except in Ampullaria, when it is converted into a con- 

 nective, going from the left commissural to the supra-intestinal gan- 

 glion." (Comptes Rendus Acad. Sc. Paris, oiii, pp. 938, 939 ; J. R. M. 

 S. (2), 1887, p. 60.) 



Nervous system of scutibranchiate gasteropods. — The nervous system of 

 various diceceous gasteropods of the groups Scutibranchiata, Aspido- 

 oranchiatia, and Cyclobranchiata has been investigated by Mr. E. L. 

 Bouvier. He found that a number of them agree in certain characters 

 and consequently proposed to combine them under a general heading as 

 scutibranchs. The common characters are stated to be as follows : 



(1) "The cerebroid commissure is very long, so that the ganglia are 

 set at the sides of the digestive tube; these ganglia are produced for- 

 wards and below to form a strong ganglionic projection, which is united 

 with that of the opposite side by a suboesophageal commissure; this 

 cord is called the proboscidial commissure." 



(2) "The stomato-gastric system arises from the inferior point of the 

 proboscidian projection and forms a loop ; the two sympathetic ganglia 

 are generally widely separated." 



(3) " The pedal ganglia are well developed and form pedal cords, 

 while the principal nerves, with which they are continuous, are almost 

 always united by transverse commissures." 



(4) " The pallial ganglia are always more or less intimately connected 

 with the pedal ganglia." 



Of these characters, the first two are regarded as being "primitive in 

 nature," and the presence of the ])roboscidian commissure, described 

 by Lacaze Duthiers in HaUotis tuherculaia^ is maintained in contradiction 

 of the statements of Bela Haller, who denied its existence. Other 

 statements of Haller are likewise traversed by Mr. Bouvier. (Comptes 

 Rendus Acad. Sc, cii, pp. 1177-1180 ; J. R. M. S. (2), vi, pp. 584, 585.) 



