VII 



MOLLUSGA~THE NEPHEW JA 



2-21 



pericardium as a simple median tube. Anteriorly it is connected with the peri- 

 cardium by a funnel, and near tlie middle communicates with the exterior l>y means 

 of a lateral urinary duct (Fig. 19, p. 12). 



C. Scaphopoda (Fig. 165, p. 193). 



Dcntalium has a pair of symmetrical kidneys, one on each side of the hind-gut. 

 Each nephridium consists of a sac provided with short diverticula. The two nephri- 

 dia are connected by a tube above the anus, and open into the mantle cavity l)y 

 two apertures at the sides of the anus. If, as maintained by all authorities, there 

 are no reno-pericardial apertures, the Scaphopoda would be the only group of Molluscs 

 in which these apertures are entirely absent. Apart from the symmetry of tlie 

 kidneys, a fact to be specially noted is that the genital piroducts pass out of the 

 genital gland into the right kidney (either by the bursting of the wall between the 

 two organs or through an aperture), and only reach the exterior, i.e. the niantlp 

 cavity, through the right renal aperture. 



It must, further, be noted that near the anus on each side, between it and the 

 renal aperture, a pore, the water-pore, occurs, the function of which is still doubt - 

 fid. If these pores really lead into the blood lacunar system of the body, as wah 

 formerly maintained, and is still held to be possible, this would be the onlj' known 

 ease of the direct imbibition of water into the blood. 



D. Lamellibranohla. 



The nephridium (organ of Bojanus) is always paired and symmetrical, and lies 

 below the pericardium and in 

 fi'ont of the posterior adductor. 

 Each nephridium is tubular or 

 sac-like, opening at one end 

 through a funnel into the peri- 

 cardium, and at the other into 

 the mantle cavity. This com- 

 nmnication of the kidney with 

 the mantle cavity always takes 

 place above the cerebrovisceral 

 connective. 



The lowest Lamellibranchia 

 {ProtoirancMa, Nucula, Lcthi, 

 SoleTwmya) are distinguished 

 in two ways. (1) Each nephri- 

 dium is a simple tube, with a 

 free cavity not traversed li}- 

 trabeculse or lamellfe. This 

 tube consists of two portions 

 which unite posteriorly at an 

 angle ; the anterior end of one 

 of these portions enters the 

 pericardium through the renal Pericardiuin 

 funnel, the other end opens venous sinus 

 into the mantle cavity. (2) 

 The paired genital glands do 

 not open outward directly, but 

 enter the kidneys near their pericardial funnel — a fact which is very important 



Pig. 184.— Transverse section through the hody of Ano- 

 donta, showing the pericardiuin, the lieart, and tlie Ividneys, 

 combined :^nd diagraniiiiatised from figures by Griesbach. 

 Not all the parts represented occur on the same section. 1, 

 2, ventricle ; 3, auricles ; 4, hind - gut ; 5, 

 6, reno-pericavdial aperture (funnel) ; V, renal 

 sac or cavity ; 8, vestibular cavity, whicli at 9 enters tlie 

 mantle cavity through tlie nepliridial aperture ; 10, genital 

 aperture ; 11, base of the foot. 



