or colour in the imago. In this way species might readily be formed 
on the ground where they actually occur, and the same general rule 
would hold as to both insular and continental areas, and, in this way, 
one can readily understand why, in some districts, large numbers of 
closely allied species maintain their distinctness. Even such a fixed 
habit as flying between 8 p.m. and 9 pan., is sufficient to isolate a 
species from an ally flying say between 7 pan. and 8 pan., and we 
know that the flight and pairing of certain species takes place 
regularly at a fixed time. In many species, the regularity of emer¬ 
gence from the pupa and of the hour at which pairing takes place, are 
so constant as to cause experienced naturalists some surprise. 
CONDITIONS NECESSARY FOR SPECIFIC DISTINCTNESS. 
I have been insisting on these particulars, because it appears to me 
that the various conditions laid down by our most eminent naturalists 
for the formation of new species under the influence of natural 
selection, are too narrowly kept between certain limits. However 
important (1) modification of structure or function, (2) the develop¬ 
ment of recognition marks, and (3) the necessity of some amount of 
infertility when crossed with allied species may be, there are other 
factors to be considered. The first of these axioms is a necessity, for 
if the newly developed form did not differ in structure or function from 
the parent form, we could not recognise it as a distinct species. There 
must be some modification of structure or function, and this modifica¬ 
tion can usually be correlated with a difference of habit, of which 
indeed it may be the result. The study of habits, then, is a useful 
addition to the work of the biologist. It appears to me that 
“ recognition marks,” and some amount of sterility, when crossed with 
allied forms,” are useful adjuncts to, but not necessities of, specific 
distinctness. 
PHYLOGENETIC AGE OF SPECIES. 
We often speak of phylogenetically new and phylogenetically 
old species, meaning thereby species that have been more recently, 
or more distantly (in point of time), evolved from a parent 
stock. If, however, we think for a moment, it must be evident 
that each species traces back its ancestry to the primeval an¬ 
cestor. of its class, and the ancestry of all species of the same 
class is, in point of time, and, from this point of view, equal. 
Some species have, however, been evolved through lines, that 
have undergone more changes than others, and, hence, some bear 
in their facies, the traces of a much more complex series of modifica¬ 
tions than others. It is these remnants of bygone conditions that 
are evident in some stage or other of the species that determine the 
super-family, family, sub-family, tribe or genus, into which we 
group the various species. It is these that make us assert that the 
Hepialids and Micropterygids are among the oldest Lepidoptera now 
in existence, meaning thereby that they are those that have undergone 
least change from the primitive form of lepidopterous insect, although 
how much modification they have undergone, we have, really no 
conception. It is these that make us say that the Sphingids and 
Geometrids are among the most specialised of Lepidoptera. 
ORIGIN OF SO-CALLED USELESS SPECIFIC CHARACTERS. 
But this long line of ancestry, accompanied as it has been, by 
endless modifications that have taken place during the aeons of time, 
