Dr. J. Gwyn Jeffreys on Black-Sea Mollusca. 425 
Mr. Distant takes at the outset of this argument is in fact 
fallacious. There is not the least warrant for the supposition 
that scent-glands or tufts have any thing to do with distaste- 
fulness. The acrid juices of distasteful butterflies are not 
generally emitted from any particular organ, but permeate all 
the tissues of the body. The fact that such organs exist in 
one sex only is strongly suggestive, if not demonstrative, of 
the view that they are secondary sexual characters; and as 
such they are regarded by Dr. Fritz Miller, who has syste- 
matically investigated these structures, and has in many cases 
actually detected the odour emitted, which is often of a pleasant 
character *. 
I have entered at some length into this discussion, because 
I am persuaded that the extension of the theory of mimicry 
proposed by Fritz Miiller marks a great advance in our views 
on this subject, which is so interesting as having been the first 
to which the Darwinian Theory of Evolution was applied with 
such success by Mr. Bates. Not only are we now in posses- 
sion of a consistent theory which enables us to dispense with 
mysterious and ‘ unknown local causes,’ but other groups of 
facts hithertoincomprehensibleare capable ofexplanation. ‘Thus 
the prevalence of one type of marking and colouring through- 
out immense numbers of species in protected groups, such as 
the tawny species of Danais, the barred Heliconias, the blue- 
black Hupleas, and the fulvous Acreas, is perfectly intelli- 
gible in the light of the new hypothesis. While the unknown 
factors of species-transformation have in these cases caused 
divergence in certain characters, other characters, viz. super- 
ficial colouring and marking, have been approximated or pre- 
vented from diverging by the action of natural selection, every 
facility having been afforded for the action of this agency by 
virtue of the near blood-relationship of the species concerned. 
When discussing the origin of mimicry, Mr. Darwin long ago 
suggested that it might have commenced at a time when the 
- species were more nearly related in marking and colouring +. 
XLV.—Black-Sea Mollusca. By J. Gwyn JEFFREYS, 
LL.D., F.R.S. 
My friend Admiral Spratt has, with his usual kindness, given 
me a few small shells, which he dredged in the Black Sea 
while surveying in 1855. None of them, except Mytilus 
* Jen. Zeit. vol. xi. p. 99; Trans. Ent. Soc. 1878, p. 211. 
+ Origin of Species, 6th ed. p. 377. 
