ZYOOBRANCHIA.] MOLLUSCA 647 The existence of two renal organs in Patella, and their relation to the pericardium (a portion of the ccelom), is br.n or/in . Diagram of a vertical antero-posterq median section of a Limpet, rs as in figs. 28, 2!>, with following additions : <y, intestine in transverse Fio. 31 Letter section ; r, lingual sac (radular sac) ; ~nl, radula ; x, lumell.ited stomach ; t, salivary gland ; tt, duct of same ; v, buccal cavity ; ir, gonad ; br.a, branchial advehent vessel (artery); br.v, branchial efferent vessel (vein); bv, blood vessel ; odm, muscles and cartilage of the odontophore ; cor, heart within tlie pericardium. (Original.) important. Each renal organ is a sac lined with glandular epithelium (ciliated cells with concretions) communicating FIG. 32. A. Section in a plane vertical to the surface of the neck of Patella through a, the rudimentary ctenidinm (Lankester s organ), and 6, the ol factory epithelium (osphradium) ; c, the olfactory (osphradial) ganglion. (After Spengel.) B. Surface view of a rudimentary ctenidiuin of Patella, excised and viewed as a transparent object. (Original.) with the exterior by its papilla, and by a narrow passage with the pericardium. The connexion with the pericar- h FIG. 33. Vertical section in a plane running right and left through the anterior part of the visceral hum]) of Patella, to show the two renal organs and their openings into the pericardium, a, large or external or right renal organ ; ab, narrow process of the same running below the intestine and lead ing by k into the pericardium ; 6, small or median renal organ ; c, peri cardium ; el, rectum ; e, liver ; /, manyplies ; g, epithelium of the dorsal sur face ; h, renal epithelium lining the renal sacs ; i, aperture connecting the small sac with the pericardium ; J-, aperture connecting the large sac with the pericardium. (From an original drawing by Mr J. T. Cunningham, Fellow of University College, Oxford.) dium of the smaller of the two renal organs was demon strated by Lankester in 1867, at a time when the fact that the renal organ of the Mollusca, as a rule, opens into the pericardium, and is therefore a typical nephridiuin, was not known. Subsequent investigations (27) carried on under the direction of the same , naturalist have shown that the larger as well as the smaller renal sac is in communication with the pericardium. The walls of the renal sacs are deeply plaited and thrown into ridges. Below the surface these Avails are excavated with blood-vessels, so that the sac is practically a series of blood-ves sels covered with renal epithelium, and forming a mesh-work within a space communicating with the exterior. The larger renal sac (re markably enough, that which is aborted in other Anisopleura) ex tends between the liver and the integument of the visceral dome Fir,. 3-1. Nervous system of Pa- It also bends round }{Jftj y ?" > r> etlal ganglion ; p, pedal nerve ; s, s , nerves (right and left) to the mantle ; o, olfac- very widely. the liver as shown 111 fig. 30, and ganglia are omitted, ce, cere- forms a large sac on half of the JS^^ffiSBS upper surface of the muscular mass c .1 f TT , i i OI the toot. Here it lies close upon the genital body (ovary or testis), and in such intimate rela- visceral loop. (After Spengel.) tionship with it that, when ripe, the gonad bursts into the renal sac, and its products are carried to the exterior by the papilla on the right side of the anus (Robin, Dall). This fact led Cuvier erroneously to the belief that a duct existed leading from the gonad to this papilla. The position of the gonad, best seen in the diagrammatic cc.pe FIG. 35. Nervous system of Haliotis ; the visceral loop is lightly shaded ; the buccal ganglia are omitted, ce, cerebral ganglion ; pl.pe, the fused plenral and pedal ganglia ; pe, the right pedal nerve ; ce.pl, the cerebro-pleural con nective ; ce.pe, the cerebro-pedal connective ; s, s , right and left mantle nerves ; ab, abdominal ganglion or site of same ; o, o, right and left olfactory ganglia and osphradiu receiving nerve from visceral loop. (After Spengel.) section (fig. 31), is, as in other Zygobranchia, devoid of a special duct communicating with the exterior. This condition, probably an archaic one, distinguishes the Zygo branchia among all Glossophorous Mollusca. The digestive tract of Patella offers some interesting features. The odontophore is powerfully developed ; the
radular sac is extraordinarily long, lying coiled in a space