214 



GASTROPODA. 



more primitive conditions found in the aquatic Pulmonates, as BHAUN has 

 shown. From this we may gather that the division of the Pulmonates into 

 Brauchiopneusta and Nephropneusta is not justifiable. It has already been 

 shown (p. 182) that we cannot regard the pulmonary cavity as a transformed 

 ureter, but must consider it as the pallial cavity, corresponding to that in 

 other Gastropods. 



The kidney now enlarges considerably and its walls become folded 

 (Fig. 98 B}. At first only a few such folds are formed, and the renal 

 cavity is still spacious, but at a later stage the lamellae almost com- 

 pletely fill it. v. ERLANGER points out that the complicated kidney 



k 



an -j*r- 



FIG. 100. An almost mature embryo of Paludina vivipara (after v. ERLANGER). <t, 

 anus ; at, auricle ; au, eye ; /, foot ; g, genital gland ; ga, efferent genital duct ; k, 

 gill ; m, mouth ; md, intestine ; mg, stomach ; mh, mantle-cavity ; mr, edge of the 

 mantle ; n, kidney ; net, ureter ; o, aperture of the ureter into the mantle -cavity ; 

 oe, reuo-pericardial pore ; op, operculum ; ot, otocyst ; pe, pericardium ; r, radular 

 sac ; sp, Spengel's organ ; st, spines on the shell ; t, tentacle ; ve, ventricle. 



of Paludina thus passes through a stage which is retained through- 

 out life by the very simple kidney of Haliotis. The opening of the 

 kidney into the efferent duct gradually approximates to the reno- 

 pericardial pore (Fig. 100). The latter is (with some exceptions) 

 known to be retained in the Gastropoda, so that the details given 

 under the Lamellibranchia (p. 74, etc.) as to the connection between 

 the coelom and the nephridia are applicable here. 



Most of the Gastropoda possess only one kidney, but those 

 Prosobranchs that are provided with two auricles ( Diotocardia, such 



