MOLLUSCA 



109 



products. On account of their position they were termed 

 by him the "capito-pedal orifices," being placed near the 

 junction of head and- foot. Spengel (24) has, however, in 

 a most ingenious way shown that these bodies are the repre- 

 sentatives of the typical pair of ctenidia, here reduced to a 

 mere rudiment. Near to each rudimentary ctenidium Spengel 



Fig. 26.— The Common lAmpet (Patella imlgata)m its shell, seen from the pedal 

 surface, x, y, .the median antero-posterior axis ; a, cephalic tentacle ; b, 

 plantar surface of the foot ; c, free edge of the shell ; d, the branchial effe- 

 rent vessel carrying aerated blood to the auricle, and here interrupting the 

 circlet of gill lamellse ; e, margin of the mantle-skirt ; f, gill lameUse (not 

 ctenidia, but special pallial growths, comparable to those of Pleurophyllidia); 

 g, the branchial efferent vessel ; ft, factor of the branchial advehent vessel ; 

 i, interspaces between the muscular bundles of the root of the foot, causing 

 the separate areas seen in flg. 27, c. (Original.) 



has discovered an olfactory patch or osphradium (consisting 

 of modified epithelium) and an olfactory nerve-gangUon 

 (fig. 32). It will be remembered that, according to 

 Spengel, the osphra- 

 dium of MoUusca is 

 definitely and inti- 

 mately related to the 

 gill - plume or cteni- 

 dium, being always 

 placed near the base 

 of that organ; further, 

 Spengel has shown 

 that the nerve-supply 

 of this olfactory organ 

 is always derived from 

 the visceral loop. Ac- 

 cordingly, the nerve- 

 supply aibrds a means 

 of testing the conclu- 

 sion that we have in 

 Lankester's capito- 

 pedal bodies the rudi- 

 mentary ctenidia. The 

 accompanying dia- 

 grams (figs. 34, 35) of 

 the nervous systems of 

 Patella and of HaUotis, 

 as determined by Spen- 

 gel, show the identity in the origin of the nerves passing 

 from the visceral loop to Spengel's olfactory ganglion of 

 the Limpet, and that of the nerves which pass from the 

 visceral loop of Haliotis to the olfactory patch or osphra- 

 dium, which lies in immediate relation on the right and 

 on the left side to the right and the left gill-plumes 

 (ctenidia) respectively. The same diagrams serve to de- 



mt 



Fig. 27. — Dorsal surface of the Limpet removed 

 from its shell and deprived of its black pig- 

 mented epithelium; the internal organs are 

 seen through the transparent body-wall, c, 

 muscular bundles forming the root of the foot, 

 and adherent to the shell; e, free mantle- 

 skirt ; em, tentaculiferous margin of the same ; 

 i, smaller (left) nephridium ; &, larger (right) 

 nephridium ; I, pericardium ; h, fibrous septum, 

 behind the pericardium ; «, liver ; int, intes- 

 tine ; ficr, anterior area of the mantle-skirt over- 

 hanging the head (cephalic hood). (Original.) 



<?— 



monstrate the Streptoneurous condition of the visceral loop 

 in Zygobranchia. 



Thus, then, we find that the Limpet possesses a sym- 

 metrically-disposed pair of ctenidia in a rudimentary con- 

 dition, and justifies 

 its position among 

 Zygobranchia. At 

 the same time it pos- 

 sesses a totally dis- 

 tinct series of func- 

 tional giUs, which 

 are not derived from 

 the modification of 

 the typical MoUus- 

 can ctenidium. 

 These giUs are in 



the form of delicate Fia. 28.— Anterior portion of the same Limpet, with 

 1 11 /£ na ■e\ ^^^ overhanging cephalic hood removed, a, ce- 

 lamellse (ng. ZO,/), phalle tentacle; 6, foot; c, muscular substance' 

 wTiiVh f nnn a Rprip<! forming the root of the foot ; d, the oaplto-peda] 

 wmcn lorm a series ^^g^%f Lankester (=rudimenWy ctenidia) ; e, 

 extending com- mantle-skirt ; /, papilla of the larger nephridium ; 

 r,lQf<>lT7 -n^n-n/l fTiQ gf, anus ; A, papffla of the Smaller nephridium ; j, 

 pieteiy rounu uia smaller nephridium ; S, larger nephridium ;!, pen- 

 inner face of the cardium ; m, cut edge of the mantle-skirt ; n, 

 IT ,1 liver ; p, snout. (Original.) 



depending mantle- 

 skirt. This circlet of gill-lamellse led Cuvier to class the 

 Limpets as Cyclobranchiata, and, by erroneous identifica- 

 ^ tion of them with 



' ^ the series of meta- 



mericaUy repeated 

 ctenidia of Chiton, 

 to associate the 

 latter Mollusc 

 with the former. 

 The gill -lamellae 

 of Patella are 

 processes of the 

 mantle compar- 

 able to the plait- 

 c " c like folds often 



Fig. 29.— The .same specimen viewed from the left observed on the 

 front, so as to show the sub-anal tract (f) of the f f j.i^ Kron 

 larger nephridium, by which it communicates with rooi OI me Dran- 

 iie pericardium, o, mouth; other letters as in flg. 28. gjijal chamber in 



other Gastropoda (e.ff., Buccinum and Haliotis). They are 

 termed pallial gills. The only other Molluscs in which 

 they are exactly represented 

 are the curious Opistho- 

 branchs Phyllidia and 

 Pleurophyllidia (fig. 57). 

 In these, as in Patella, the 

 typical ctenidia are aborted, 

 and the branchial function *** 

 is assumed by close -set 

 lamelliform processes ar- 

 ranged in a series beneath 

 the mantle- skirt on either 

 side of the foot. In fig. 26, 

 d the large branchial vein of 

 Patella bringing blood from 'ksi' 



tlio (lill apripa tn tViP l|port FiO- 30-— Diagram of the two renal organs 

 tne glU-serieS to me neart (nephridia), to show their relation to the 



rectum and to the pericardium. /, pa- 

 pilla of the larger nephridium ; g, anal 

 papiUa with rectum leading from it ; hy 

 papilla of the smallernephridium, which 

 is only represented by dotted outlines ; 

 I, pericardium indicated by a dotted out- 

 line, — at its right side are seen the two 

 reno-pericardial pores ; Jf, the sub-anal 

 tract of the large nephridium given off 

 near its papilla and seen through the 

 unshaded smaller nephridium ; ks.a, an- 

 terior superior lobe of the large ne- 

 phridium ; ks.l, left lobe of same ; lcs.p, 

 posterior lobe of same ; fcs.i, inferior 

 sub- visceral lobe of same. (Original. ) 



ksl 



IS seen ; where it crosses 

 the series of lamellse there 

 is a short interval devoid 

 of lameUse. 



The heart in Patella con- 

 sists of a single auricle (not 

 two as in Haliotis and Fis- 

 sureUa) and a ventricle ; the 

 former receives the blood 

 from the branchial vein, the 

 latter distributes it through a large aorta which soon leads 

 into irregular blood-lacunse. 



