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THE AMERICAN NATURALIST [Vol. XL 



a second ring around the margin of the mantle at the base of the 

 glandular zone. 



4. The horizontal interfascicular vessels (Quervenen of Haller), 

 a series of vessels which cross the columellar and pallial muscles 

 connecting the perivisceral and the internal pallial trunks. 



5. The vertical interfascicular vessels, a series of vessels which 

 run up from the foot in the columellar muscle, join each with a 

 horizontal interfascicular vessel and so connect with the internal 

 pallial. 



G. The mantle plexus. This consists of a dorsal and a ventral 

 network. The vessels of the ventral network arise from the inter- 

 nal ])allial trunk and the ultimate branches end blindly in the 

 glandular zone. The vessels of the dorsal network arise from the 

 external pallial trunk and end blindly in the non-glandular zone 

 of the mantle. In a view such as we are describing the two net- 

 works are indistinguishable. 



7. The transverse pallial vessels. One or two vessels, which 

 arise from the external pallial trunk opposite the left end of the 

 columellar muscle, unite (if two are present) and curve around the 

 muscle to the auricle. In a relaxed specimen such as we are de- 

 scribing they cannot be traced to the auricle but in a perfectly 

 fresh animal their pulsation is readily seen. 



8. Indications of a suprarenal plexus (periiniestinales Venen- 

 netz of Haller). The distal ends of the nephridial cceca are grown 

 to the dorsal body wall and the blood sinus in which they lie is 

 thus broken up into a series of connecting spaces. 



9. Supravisceral vessels, which ramify over the dorsal surface 

 of the digestive gland and open eventually into the suprarenal 

 plexus. I have been most fortunate in finding these dorsal vessels 

 showing clearly in specimens preserved in Gilson's fluid in which 

 the contraction had been reduced to a minimum either by nar- 

 cotizing with chloretone or by slitting the muscles of the foot. 



10. Ctenidial vessels. In a preserved specimen one may see 

 through the wall of the nuchal cavity the ctenidium with its dorsal 

 series of lamella' and the all'erent and efferent vessels running 

 respeetivelv :.l,>nu ii- ri^h, posterior) and left (anterior) edges. 

 The allerent vessel brino-^ blood U-om the suprarenal plexus, the 

 efferent one carries it to the auricle. At the base of the gill may 



