5» SCIENCE PROGRESS. 



partial acceptance to both these views. For the nervous 

 system of Mollusca appears to me to consist of two parts, a 

 circumferential ring and a peri-blastoporal plexus. The 

 circumferential ring, which was primitively associated with 

 a ciliated ring, is represented by the pleuro-visceral nervous 

 system, which I have shown to possess significant relations 

 with the velum or prototroch of the larva ; and the peri- 

 blastoporal plexus seems to me to be recognisable in the 

 pedal nervous system, which in primitive Molluscs has a 

 very diffuse plexus-like arrangement, and in Amphineura, 

 at any rate, reveals its peri-blastoporal character in the 

 cerebro-pedal connectives in front and its connectives with 

 the supra-rectal abdominal ganglion behind. 



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