336 Mr. E. R. Lankester on the Anatomy of the Limpet. 



on the upper surface of the liver-mass, but does not completely 

 enclose it. This sac has a dark greenish-brown pulverulent 

 tissue, which is to a certain extent laminated ; and from its 

 orifice quantities of a dark powder can be forced. It is not im- 

 probable that water distends this sac when the limpet is in a 

 state of expansion, and that the liquid which oozes from the 

 animal when touched on its rock, exudes from the infraanal or 

 supraanal orifice. 



By most careful dissection. Dr. Rolleston and myself detected 

 what appears to be a minute opening from the pericardium into 

 the supraanal articulated sac, lying in the curve of the rectum. 

 The orifice I found first by opening the pericardium, when it 

 was seen between the bifurcation of the auricle at the right side 

 of the cavity, and was then traced from both the pericardium 

 and supraanal sac in other specimens. 



Comparing this with Mr. Hancock's description of the renal 

 organ of Nudibranchs, it is found that they diflfer chiefly in that 

 Patella retains the double character of the organ to a greater 

 extent than do the Nudibranchs ; and this is what might be 

 expected from the bilateral symmetry exhibited in other parts 

 of its organization, — e. g. the capito-pedal orifices and the dis- 

 position of the gills. The small supraanal sac communicating 

 with the pericardium may be compared to Mr. Hancock's 

 " pyriform organ ;" but it diifers in having a sepai-ate commu- 

 nication of its own with the exterior, thereby retaining its cha- 

 racter as the left half of Bojanus's organ. The infraanal or 

 right sac and orifice, on the other hand, undoubtedly corre- 

 sponds to the dendritic glandular sac and orifice of Doris, Bor- 

 nella, &c. Any comparison of adult structures must, however, 

 necessarily be very unsatisfactory in animals which have under- 

 gone such different modifications asLamellibranchs,Prosobranchs, 

 and Nudibranchs ; and we can only guess at homologies until 

 the development in each case is fully understood. 



As to the absence of oviducts or sperm-ducts, I can most 

 fully confirm MM. Robin and Lebert, Dr. Rolleston having 

 most carefully tested my conclusions on this point before we 

 had seen the paper of the French naturalists. 



Reverting again to the capito-pedal orifices, I may just ob- 

 serve that their opening into a blood-sinus is not a little re- 

 markable, calling to mind the discoveries of M. Lacaze-Duthiers 

 as to orifices bringing water from the exterior into the branchial 

 veins of Tethys, Pleurobranchus, &c. Whether such be their 

 function, or whether, as seems most probable, they are genital 

 pores, I cannot say. Chiton, which is allied to Patella very 

 closely, forms a notable exception to the rule of an asymmetrical 

 genital pore among Gasteropods, having two bilaterally sym- 



