87 
insects are allied the closer resemblance there is in the secondary 
sexual characters. All this seems at first sight to point to hereditary 
descent from a common ancestor, seeing that the characters have 
apparently no use, and that the less the species have diverged the nearer 
the secondary sexual characters are to each other ; and yet I am by no 
means assured that this is the true explanation, and I am always loth 
to put anything down to this cause when another solution is possible, 
and there are many difficulties in the way of solving the question by 
assuming that they are relics of once useful structures. There is one 
point here that I wish to emphasise, and that is, that the common 
practice of classing all these kind of characters as being rudimentary 
remnants of once useful structures is neither a scientific nor satis¬ 
factory way of settling the matter, as it simply but effectively puts the 
closure on the whole question at once, and in a way that admits of very 
little chance of discussion at any future time. I do not, of course, say 
there are no vestigial or rudimentary characters, because there are no 
doubt plenty of them, but I certainly think it should be the last resort 
of enquiry and not the first, as is so often the case. It is such an 
easy way of settling everything that is not of obvious use, but, on the 
other hand, it gives an outsider the idea that evolution has come to a 
stop, and that everything we see are degenerated species, which show 
us nothing but relics of structures whose usefulness came to an end 
some time back. The fact that the struggle is greater than ever, and that 
nature is producing new structures and new combinations continually, 
must, I think, be patent to everyone, and if we lay ourselves open to 
misunderstand all these structures as soon as they come under our 
notice, what chance have we of understanding the laws which govern 
their production. When one sees the effects of the struggle for exist¬ 
ence in the species which have so far modified their habits as to use 
our civilisation as a means of getting an easier livelihood —Anobium 
paniceum is a case in point, to which nothing in the way of dried food 
comes amiss, Dermestes lardanus is another, Attagenus pellio, &c., and 
there are plenty of examples in lepidoptera and other orders as well 
where insects feed on artificial diet in houses and warehouses—I look 
on this as one of the most convincing of all ocular demonstrations of 
the struggle going on around us, which we can prove so logically and 
yet see so little of its actual reality. 
I will point out one of the difficulties that present themselves to 
the mind in connection with the subject. The genus Pterostichus is a 
group of closely allied beetles, and in this group there are several 
coming close together, which have in the $ s small but distinct 
secondary sexual characters on the last visible ventral segment of the 
abdomen. In P. niger it takes the form of a small longitudinal ridge, 
in P. anthracinus it is a minute tubercle, in P. minor it is a fine 
longitudinal raised line, in P. madidus it is a transverse ridge, and in 
P. aethiops it is an obtuse tooth. It will be clear to anyone that all 
these characters are closely allied, and they are mostly small, obscure, 
and of no apparent use to the possessor. At all events it is difficult to 
assign the use that a longitudinal ridge has to an insect, when in a 
closely allied species it is a transverse ridge, and in a third species it is 
neither transverse nor longitudinal but only a tubercle, while in another 
species it is not raised at all but is a depression, and our easy way out 
of the difficulty is to simply say they are the relics of a character which 
