474 J. F. ILLINGWORTH 



the anterior mantle nerves (Mn). It is a question whether we should 

 continue to call these the mantle nerves, since finding their relation 

 to the circum-pallial chord. It seems to me that they are of secondary 

 importance, and only a little better than the pleuro-pallial connectives. 

 Of course they have a somewhat different relation, being joined to 

 the gill ganglia. 



Each little ganglionic centre of the posterior two thirds of the 

 mantle ring nerve receives a pleuro-pallial connective, and gives off a 

 nerve to the outer part of the mantle (Fig. D). This latter nerve 

 branches almost immediately, the larger part continuing out to the 

 edge of the mantle, the other bending upward, and sending nerves to 

 the mantle above and below the shell. 



Summary. 

 A few of the most important points which have been described 

 in detail in the text will be taken up here, following their natural 

 order. 



1) The epipodium is rudimentary and the nerve going to it also 

 very weak. 



2) The pharynx is enlarged into a great crop-like pouch contain- 

 ing the many folded digestive glands. 



3) The stomach has three large, distinct hepatic ducts enter- 

 ing it. 



4) The nephridia are very unsymmetrical. Both have external 

 openings. The right has an indirect reno-pericardial duct. 



5) The oviduct opens just within the external papilla of the 

 right kidney. 



6) The reno-pericardial duct is a short tube leading from the 

 right side of the pericardial cavity, and opening into the oviduct. 

 The epithelial cells lining the duct are very large, and have exceed- 

 ingly long ciHa. 



7) The shell muscles are distributed along the margin of the 

 shell and are very weak. 



8) The vascular system is a closed circulation. 



9) There are two auricles, with a ventricle between them. 



10) Joining the ventricle is a large, rectangular, aortic chamber. 

 Three aortae are given off from this, an anterior or buccal, a gastric, 

 and a posterior or genital aorta. 



11) The mantle circulation is well developed. The blood is 

 distributed by a palliai artery, that surrounds the body and returns 



