674 MB. J. GEAHAM KBER OK THE [Jufle 18, 



to both these statements, Professor Lankester seems to be in error, 

 as a complicated buccal system was described and figured by H. v. 

 Jhering \ while at least part of an enteric system was described by 

 Xeferstein-. In i-egard to the buccal nervous system it seems 

 advisable to give a short account, however, as von Jhering's remarks 

 are very brief, while in the construction of his diagram a curious 

 blunder seems to have been made, which has been perpetuated 

 by its being copied by leading text-books. In effect, what he 

 figures as the cerebro-pharyngeal connective is really the forward 

 prolongation of the pharyngeal ganglion, which, uniting with its 

 fellow in the middle line, forms the anterior infra-buccal com- 

 missure. On the other hand, the two nerves figured as emerging 

 from the pharyngeal ganglia laterally are the cerebro-pharyngeal 

 connectives, of which there are not one, but two, on each side. 

 In fact, by rotating the portion of his figure representing the 

 buccal nervous apparatus through 180° about an axis passing 

 tlu'ough the pharyngeal ganglia and joining up the cut ends as 

 indicated above, one gets quite an accurate diagram. No doubt 

 V. Jhei'iug's slip arose through dissecting and figuring this part of 

 the nervous system after the buccal mass had been removed from 

 its connection with the animal. 



The cerebro-pharyngeal connectives are two thick nerve-trunks 

 on each side, taking their origin from the adoral border of the 

 supra-oesophageal nervous mass. Enclosed in a dense sheath of 

 connective tissue, they pass to the sides of the buccal mass. For 

 the first part of their extent their course is highly sinuous, a 

 character probably to be connected Avith the protrusibility of the 

 buccal mass and the consequent very variable distance between it 

 and the fixed circum-cesophageal parts of the nervous system. 

 Pursuing a slightly convergent course the two connectives reach 

 the lateral aspect of the buccal mass, and there unite in the 

 pharyngeal ganglion (fig. 4, xili.g.) — a triangular structure with 

 its apex directed towards the mouth — and another of its angles 

 external. It lies on the muscles of the buccal mass immediately 

 beneath the skin. 



The two pharyngeal gangHa are connected to one another by a 

 longer anterior and a shorter posterior commissure, on the course of 

 the latter being the slightly swollen " buccal ganglia." The anterior 

 commissure (fig. 4, ant.com.), figured by v. Jhering as cerebro- 

 pharyngeal connective, is a flattened band nearly 1 millimetre 

 in breadth, and pursuing a fl-shaped course immediately beneath 

 the skin, and just within and parallel to the margin of the lower 

 mandible. As the ganglion tapers off into the commissure, it givea 

 off numerous small and several larger filaments to the skin-fold 

 surrounding the mandibles. From the adoral part of the com- 

 missure also some very fine strands pass off to the same structures. 



The internal angle of the pharyngeal ganglion is prolonged 

 towards the middle line into the posterior commissure, which soon 



1 Vergl. Anat, des Nervensystems der Mollusken, p. 263. 

 - Bronn's ' Thier-Reich,' Malacozoa, p. 1373. 



