52 
this question. I have attempted to describe the secretion as aceu- 
rately as possible, but have not been able to make a chemical ana- 
Iysis nor to detect any crystalline elements in it. Still these ne- 
gative results do not forbid any such interpretation and it must on 
the contrary be remarked that the strongly refracting spherical 
globules above mentioned, which the apparatus secretes, can 
hardly be looked upon as being a mucus-like substance and on the 
contrary resemble the renal secretion of many other Mollusks. 
Moreover in the similarly situated organs in C'haetoderma , which also 
place the pericardium in communication with the exterior — although 
along a foreshortened route when compared to Proneomenia — HANsEN 
has observed distinet erystals, and although he describes and figures 
them as slime glands he nevertheless suggests that these organs might 
perhaps be looked upon as kidneys. 
If we suppose for a moment for Proneomenia this hypothesis to 
be really definitely proved — and with a richer material of spe- 
cimens this might present little difieulty — the urogenital appar- 
atus of this genus appears to us highly suggestive and of special 
‘ morphological interest. We then find in this archaie Mollusk a 
primitive condition which the higher Mollusks have probably pas- 
sed through, but which has become modified and differentiated in 
the most divergent directions in the different groups. This primi- 
tive condition can thus be briefly sketched: By a pair of ciliated 
ducts the genital products are discharged into the body-cavity (pe- 
ricardium). From thence they are conveyed by paired ciliated ducts 
into the interior cavity of the kidney (nephridium) which is paired 
in its anterior, coalesced in its posterior portion. In this way the 
kidney and the pericardium are in open communication. And so 
the genital gland, the pericardium and the kidney which in 
other Mollusks show different degrees of mutual connexion and in 
the higher developed forms are wholly independent from each 
other, lead one into anotherin the Solenogastres in an unbroken 
order of succession. 
In the Solenoconchae, in certain more primitive Gastero- 
poda (Patella, Fissurella),, and in those Lamellibranchia that 
