Miscellaneous. 413 



an orthoneurous visceral commissure, upon wliich we may imagine, 

 to be concise, two symmetrical pallio- branchial ganglia, innervating 

 symmetrically the gill and the mantle of the same side. The whole 

 of this symmetrical apparatus has been transported, owing to the 

 peculiar mode of growth, to the right and towards the front, and 

 has filially come to occupy a symmetrical dorsal position, as we 

 stiU find it in FissureUa. The primitive right gill is therefore found 

 to the left, and the left to the right; moreover, since the gills carry 

 with them the ganglia which innervate them, the visceral com- 

 missure became chiastoneurous. Later on the right gill (primitive 

 left) atrophied, and Gastropods were produced provided with the 

 single left gill (primitive right) such as we find in the great 

 majority of the Prosobranchia and also in Acttfon. 



Eut then there took place a displacement of the gill in precisely 

 the opposite direction. The persisting left gill returned towards 

 the rear and to the right, carrying with it its ganglion (the supra- 

 intestiual) and the supra-intestinal commissural branch, which 

 came to lie on the right side of the oesophagus. 



The branchial ganglion (primitively supra-intestinal) probably 

 became fused with the right secondary pallial ganglion ; it no longer 

 sent nerve-branches into the left portions of the mantle, which were 

 too far off, but it innervated the regions of this organ which are 

 situated to the right, that is to say in the neighbourhood of the giU. 

 The subintestinal ganglion, having become useless, atrophied alto- 

 gether, at the same time as was developed the left secondary pallial 

 ganglion, which carried to the left of the a3sophagus the subintestinal 

 commissural branch, and assumed the sole control of the innervation 

 of the left portions of the mantle {Acera hullata and aquatic Pul- 

 monata). In the other Opisthobranchiate forms the left secondary 

 pallial ganglion has approached much nearer to the visceral ganglion 

 or has even become fused with it. In all cases the visceral com- 

 missure has become more or less decidedly orthoneurous, and this 

 arrangement has enabled the nervous centres situated upon the 

 commissure to approach one another very nearly, and even to fuse 

 together (Nudibranchia, certain Pteropoda, and terrestrial Pul- 

 monata).' The Pulmonata are directly connected with the Actajonidte 

 by their branchiferous {kiiphonaria) and opercalate (AnvphiboJa) 

 species, and there can no longer be any question of establishing in 

 the class Mollusca two parallel series independent one of the other, 

 — Comptes Bendus, t. cxvi. no. 2 (January 9, 1893), pp. 68-70. 



On the Branchial Sense-Oiyans of the Patellidoe. 

 By Dr. J. Thiele, of Dresden. 



When I was examining some time ago a series of transverse 

 sections which I had prepared of a specimen of Patina peUucida, my 

 attention was attracted by a button-shaped projection of the epithe- 

 lium at the sides of the body between the foot and mantle which 

 could hardly be anything else than a sense-organ. For the moment 



Ann. & Mag. N. Hist. Ser. 6. Vol xi. 30 



