740 JOURNAL, BOMBAY NATURAL HIST. SOCIETY, Vot. XXVIII 
finally the twigs are placed over the branchlets. Thus we manage to arrange the 
twigs or species in a reasonable order. It seems very easy, but unfortunately 
all that is left of our ti’ee, which has been growing for millions of years, are 
just a few of the tv'igs. In some of the other branches of Natural Historj' the 
Geologist can help the Zoologist to reconstruct their trees by means of fossils, 
but, as may very well be imagined, he can give us no assistance -vvorth the name 
with our tree. Thus it may be seen that the problem of butterfly classification 
is extraordinarily dififlcult, since all we have to go upon is the study of present 
day conditions, our knowledge of which may be said to have attained respec- 
table dimensions since the days of the pioneer Linnaeus at the end of the 
eigteenth century, but, as stated in my former paper, far more remains to be 
done especially in India. 
3. The species Ls the basis of classification, but what constitutes a species is 
not so easy to define. Bingham in his volumes in the Fauna of India Series on 
the butterflies discarded the word as it was so open to misconception and used 
the word “ form ” instead. I think it is now generally accepted that, when 
two so-called forms fly together and do not interbreed, they are to be regarded 
as species ; where they do not fly together and present well defined differences, 
it is a matter of opinion whether they are to be regarded as species or geogi'a- 
phical races ; usually if they are structurally similar and of similar habits, it 
is probably prefsrable to regard the two forms as races, otherwise they should 
be treated as species. A number of allied species are grouped for the sake of 
convenience into what is called a genus. Usually butterflies that differ in struc- 
ture are placed in seiiarate genera, but no hard and fast rule can l>e laid down, 
since certain obviously closely allied species differ materially from each other 
in this respect, as also do rarely individuals of the same species, while cases are 
by no means unknown where the structure of the wings on one side differs from 
that on the other side. Some Naturalists divide genera into sub-genera, but 
except perhaps in the case of some of the larger and more unv«elcly genera this 
elaboration is undesirable. Genera are further grouped into sub-families and 
families. A reference to the diagram in paragraph 2 will indicate how the 
families, genera and species correspond to the branches, branchlets and twigs 
of the butterfly tree. 
4. Without the history of the past to aid him, it will be realised that the 
Naturalist is groping in the dark w'hen he tries to discover the natural order in 
which butterflies should bo placed. All he can do is to examine the features 
of each species ; to ascertain and tabulate the differences between them in res- 
pect of every know'n character ; to decide w'hat value is to be placed on the 
differences that he has found and finally to adojet a grouping and order that 
appears most natural. Amateurs are ahvays blaming the so-called cabmet 
naturalist for changing the classification and nomenclature ; I share their an- 
noyance when some delver into the records of the past enforces what is called 
the law of priority, that is to say, changes a name because he has found that 
some defunct naturalist had produced some other name prior to the date on 
which the one in current use had been coined. But when the change is neces- 
sitated by a well founded advance in knowledge, the objection is a foolish one. 
The essential point to bear in mmd is that no hard and fast rules can be laid 
down for the definition of a species, genus, or family or for the value of any 
particular feature ; again and again a character that has been considered above 
reproach for defining species, etc., has turned out to be a snare and a delusion. 
The consensus of opinion of the best naturalists of the day is the only guiding 
principle that can be followed. I am afraid that the leading experts often 
differ a good deal, but at least the main principles of butterfly classification 
have now been settled. 
.5. Having outlined the principles of the system of classification in vogue 
aad its limitations, it is now' necessary to consider the various characters on 
