Miscellaneous. 413 



an orthoneiirous visceral conimissure, upon wliich we may imagiiio, 

 to be ronciso, two symuiitrical pallio-brancliial ganglia, innervating 

 syninietrically the gill and tlie mantle of the same side. The whole 

 of tliis symmetrical apparatus has been transported, owing to the 

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

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

 still find it in Fissurella. 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 thom, the visceral com- 

 missure became chiastoueurous. Later on tho right gill (primitive 

 left) atroi)hicd, and CJastropods were produced provided with the 

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

 majority of the Prosobranchia and also in Acheon. 



15ut then there took place a displacement of the gill in precisely 

 the opposite direction. Tho persisting left gill returned toward^ 

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

 intestinal) and the supra-intestinal commissural branch, which 

 came to lie on the right side of the oesoi)hagus. 



The branchial ganglion (primitively supra-intestinal) probably 

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

 sent nerve-branches into the left ])ortious of tlie 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 gill. 

 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 oesophagus the subintestinal 

 commissural branch, and assumed the sole control of the innervation 

 of the left portions of the mantle (Accra 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 tlie 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 (Xudibranchia, certain Pteropoda, and terrestrial Pul- 

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

 by their branchiferous (SijJtonaria) and operculate (AmpJiiboIa) 

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

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

 — Com})tes Rendus, t. cxvi. no. 2 (January 0, 1893), pp. 68-70. 



On the Branchial Sense-Or(jans of the Patellida?. 

 By Dr. J. Thiele, of Dresden. 



When I was examining some time ago a series of transverso 

 sections which I had prepared of a specimen of Patina pellucida, 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 



Anri. d' Mag. X. Hist. Ser. 6. Vol. xi. 30 



