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 differ 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 differs in having a separate 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 as Lamellibranchs, 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- 
