may be interpreted as meaning : 1) that it is on the verge of disap- 
pearing altogether, and 2) that in Natal the corresponding interme- 
diate formerly existed, but has now disappeared. The significance 
of the occurrence of intermediates as well as of their frequent rarity 
is evident. The absence of intermediates between the forms of di- or 
polymorphic species is now and again brought forward as an argu- 
ment in favour of the origin of these individual forms fer saltum. 
In a survey of all the polymorphic Butterflies, however, it will be 
found that the absence of intergradations is the exception rather 
than the rule.It must also be borne in mind that it is generally due 
to chance that scarce intermediates fall into the hands of the col- 
lector in the tropics and that they may be absent from the locality 
visited and not particularly scarce in another. The variability of a 
species, as every field-collector knows, varies in different stations, 
often considerably, and it depends much on accident whether one 
comes across the locality where a species exhibits the widest range 
of variation. The absence of intermediates from our collections is 
therefore no proof that such individuals do not exist. Moreover, 
the range of variability exhibited by the comparatively few speci- 
mens which come under the eyes of the systematist, is in many 
cases much inferior to that shown by the same species under 
abnormal conditions of life, as is proved by the results of temper- 
ature experiments. 
As the intermediates are opposed to the assumption of the origin 
of the forms fer saltum, it appears to me evident in view of the 
above facts that « mutations » are merely forms which appear 
separated by a gap because the intermediate characters have dis- 
appeared or are suppressed. Anyhow, the theory of discontinuous 
mutations does not apply to the phenomena we have under 
consideration, on account of the intermediates to which I have 
constantly drawn your attention in the course of this address. I may 
mention in passing that very instructive series of connecting links 
between the individual forms are known in the American Papilio 
glaucus and Papilio hectorides, the African Papilio dardanus, and 
the Oriental Papilio rumanzovia, and that there also occur 
intermediates between some of the female-forms of the Oriental 
Papilio polytes and Papilio egeus ormenus. And it is perhaps also 
not superfluous to reiterate in this connection that the geographical 
races, too, are nearly always found to be connected by intergrad- 
ations, if a sufficiently large number of specimens is examined. 
Since the theory of abrupt mutations does not fare well here at 
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