no 



MOLLUSCA 



The existence of two renal organs in Patella, and their 

 relation to the pericardium (a portion of the ccelom), is 



ear I 



Fjg. 31. — Diagram of a vertical antero-postero median section of a Limpet. 

 Letters as in figs. 28, 29, witli following additions : q, intestine in transverse 

 section ; r, lingual sac (radular sac) ; rd, radula ; s, lamellated stomaGh ; t, 

 salivary gland ; w, duct of same ; i?,- buccal cavity ; w, gonad ; Jw.o, brancMal 

 advehent vessel (ar1:ery) ; ^r.«, brancMal efferent vessel (vein) ; Zw, blood- 

 vessel ; odm, muscles and cartilage of the odontophore ; cor, heart within the 

 pericardium. (Original.) 



important. Each renal organ is a sac Uned 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 ctenldium (Lankester's organ), and 6, the ol- 

 feetory epithelium (osphradium) ; c, the olfectory (osphradial) ganglion. 

 (After Spengel.) B. Surface view of a rudimentary ctenidium 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- 



Fia. 33. — Vei'tical section in a plane running right and left through the 

 anterior part of the visceral hump of Patella, to show the two renal organs 

 and tiieir openings into the pericardium, a, large or external or right renal 

 organ ; db, narrow process of the same running idow the intestine and lead- 

 ing by k into the pericardium ; b, small or median renal organ ; c, peri- 

 cardium ; d, rectum ; e, liver ; /, manyplles ; g, epithelium of the dorsal sur- 

 face : ft, renal epithelium lining the renal sacs ; i, aperture connecting the 

 small sae with the pericardium ; fc, 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 nephridium, 

 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 waUs 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 Fiq. 34.- 

 very widely. It also bends round '""' ' 

 the Hver as shown in fig. 30, and 

 forms a large sac on half of the 

 upper surface of the muscular mass 

 of the foot. Here it lies close 

 upon the genital body (ovary or 

 testis), and in such intimate rela^ 

 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 (Eobin, Dall). 

 This fact led Cuvier erroneously to the belief that a duct 

 existed leading from the gonad to this papiUa. The 

 position of the gonad, best seen in the diagrammatic 



-Nervous systfim of Pa- 

 tella; the visceral loop is 

 lightly shaded ; the buccal 



fanglla are omitted, ce, cere- 

 ral ganglia ; c'e, cerebral com- 

 missure ; pi, pleural ganglion ; 

 pe, pedal ganglion ; p'e, pedal 

 nerve ; s, s', nerves (right and 

 left) to the mantle ; o, olfac- 

 tory ganglion, connected by 

 nerve to the Streptoneurous 

 visceral loop. (After Spengel.) 



Fig. 35.— Nervous system of HaUotis; the visceral loop is lightly shaded; 

 the buccal ganglia are omitted, ce, cerebral ganglion ; pl.pe, the fused pleural 

 and pedal ganglia ; pe, the right pedal nerve ; ee.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 olfectory 

 ganglia and osphradia 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 aU 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 



