ANATOMY AND PHYSIOLOGY OF PATELLA VTTLGATA. 605 



the visceral mass. Posteriorly to the rectum, and supporting it, lies the genital 

 organ (male or female), which at certain seasons is very large, and forms a 

 crescentic mass, on surface view, enclosing and supporting the other organs. 

 It is wedge-shaped, and extends along the floor of the visceral cavity, its thick 

 edge forming the crescent above mentioned. 



Between the rectum and the genital gland, and spreading round the former 

 and sending projections over the latter so as to enclose it, is the posterior 

 portion of the right nephridium. It may be traced as a dark brown mass pass- 

 ing up the right side. It is very variable in form, sometimes scarcely apparent 

 on surface view, at other times ramifying extensively over the dorsal surface. 

 It varies in colour from a brown yellow to a deep burnt umber. On the extreme 

 right may occasionally be seen a portion of the lingual ribbon in its sheath. The 

 right nephridium usually extends for f of the circumference of the visceral mass. 



The centre of the visceral dome is occupied by the liver, a granular villous 

 mass of yellowish-green colour. It is enclosed by a coil of intestine, which 

 springs from and ends at the right side, and which separates it from the right 

 nephridium. Between the anterior bend of this coil and the rectum lies a branch 

 of the right nephridium. 



Anterior to the rectum, and between it and the anterior boundary ridge, 

 there is a quadrilateral region, which is divided into two by a fibrous septum. 

 That part, usually more or less triangular in outline, lying nearer to the anal 

 end of the intestine, is entirely occupied by a light brown body, the left 

 nephridium. The rest of the space is white and fibrous in appearance, and 

 forms the dorsal wall of the pericardium. The visceral integument is free from 

 the viscera, save where it lies upon the nephridia and pericardium, with both of 

 which it is intimately connected. 



Born and Reeve, among the older naturalists, give the fullest accounts of 

 the external features, the former in his Testacea Mus. Cces. Vind., the latter in 

 his Conchologica Iconica. Cuvier gives a short description of the soft parts 

 visible without dissection (Memoires pour servier a VMstorie et Vanatomie des 

 Mollusques). Gwyn Jeffreys (British Conchology) gives the most complete 

 recent account, but errs in saying that the shell is opaque. None of the shells 

 examined by the writer were altogether opaque ; the majority were translucent, 

 though some were less so at the apex than elsewhere. 



2. Alimentary System. — The alimentary system is very complicated, and 

 has not hitherto been investigated in any detail. The following account does 

 not profess to be perfectly complete, either macroscopically or microscopically ; 

 and the difficulties in the way of a thorough and accurate examination of all 

 the parts are such that it cannot profess to be final either. Many points yet 

 require a more detailed investigation, which the writer means to undertake in 



