THE MORPHOLOGY OF THE MOLLUSC A. 43 



ago. Since the mantle-lappets of the two sides of the body 

 unite posteriorly above the anus, this pallial nerve-ring lies 

 above the gut. The ring is connected with the cerebro- 

 pleural ganglia by means of the anterior pallial nerves, and 

 with the visceral (parieto-splanchnic) by means of branches 

 from the great posterior pallial nerves. Accordingly Thiele 

 homologises the circumpallial nerve-ring with the lateral 

 cords of Chiton and with the epipodial plexus of the Rhi- 

 pidoglossa. 



The first of these homologies seems not unreasonable, for 

 no one disputes the homology between the mantle of Chiton 

 and that of Pelecypoda. Moreover Kowalevsky's discovery 

 that Chiton in its later embryonic phases is provided with 

 a pair of transitory eyes which lie outside the velar area 

 and have some close connection with the lateral nerve- 

 cords, renders this comparison particularly worthy of 

 attention. But how the circumpallial nerve of Pelecypoda 

 can be in any sense homologous with the epipodial plexus 

 of Gastropoda, when the latter structure lies beneath the 

 gut and has no connection with the cerebral ganglia, either 

 directly or by the intermediation of the pleural ganglia, it 

 is altogether impossible to conceive. And this is not all. 

 The posterior connection between the circumpallial nerve 

 of Pelecypoda and the visceral ganglia is compared by 

 Thiele with the posterior connectives between the lateral 

 and ventral cords of Amphineura ; and the time-honoured 

 visceral nerve-cords of Pelecypoda, with the visceral (parieto- 

 splanchnic) ganglia upon them, are homologised with the 

 ventral cords of the Amphineura. To reveal the absurdity 

 of these comparisons it is sufficient, I think, to remind my 

 readers that the ventral cords of Chiton are concerned ex- 

 clusively with the innervation of the musculature of the 

 foot ; while the visceral cords of Pelecypoda innervate 

 the body-wall, ctenidia and viscera^ in addition to the 

 posterior adductor muscle. How these supposed homo- 

 logues of the ventral cords of Chiton have come to assume 

 so many of the functions of the lateral or pallio-visceral 

 cords, is not explained ; and since Pelecypoda possess a 

 pair of pedal ganglia in the foot, as typical in their relations 



