34 
MEMOIRS OF THE XATIOXAL ACADEMY OF SCIENCES. 
terial spine or hooks are developed. The cremaster affords excellent generic and specilic characters. 
In the subterranean pnpa of Datana it is present^ and is of use in aiding the pui^a to reach the 
surface of the ground. It is very large and acute in the subterranean pupm of Ceratocainpidm 
and Sphinges. It is evident that in the presence or absence of the creinastei’j and in its shape 
and in the number of hooks and their sliapCj \ve have a set of very idastic characters (though 
excellent for distinguishing genera and species) whose variability' and plasticity is due to the 
varying habits of the pupa, wiietlier living above or under ground, whether protected by a very 
thin, loose, net-like cocoon or by a solid double one like that of Cerura or of the silkworms. Also 
whether the thread is continuous and can be readily reeled, as in Bomhyx moriy or whether the 
thread is often interrupted at the anterior end, as in Flatysamia recropidy is a feature which was 
probably the result of a slight change of circumstances and may have been inaugurated as the 
result of variation in a single individual during a single lifetime, afterwards in succeeding genera- 
tions becoming hxed by homochroiiic inheritance. 
3. Imago state , — It is easier to select what may have been acquired characters in caterpillars 
than in butterdies and moths, and yet the latter have a complicated series of what may originally 
have been acquired characters. It should be borne in mind that while caterpillars live for weeks 
and even months, are subject to frequent Jiiolts, are active, and are dependent on a proper sup])lyof 
their food, usually this or that plant, butterflies and moths perish, as a rule, directly after mating, 
taking little or no food. Of course acquired characters are most marked in the parts which are 
most iTsed, as the maxilla?, wings, and external genital armature. 
The absence of maxillic or their very rudimentary condition in Bombycine moths is, with little 
doubt, a recently acquired character. The very arbitrary distribution in Lepidoptera of scent 
organs (Androconia, etc.) are apparently characters recently acquired. The wonderful variations 
in the markings of the wings, due to a variety of slight causes, may often arise during an indi- 
viduaPs lifetime and become a matter of inheritance, the result of sudden changes in temperature, 
moisture, or dryness, and changes in food of the larva. By stibjecting individual i)upie to pro- 
longed cold, -or vice versay varieties and a greater or less number of broods may be produced 
artificially, and this may illustrate how seasonal varieties have arisen in nature. 
Mau}^ species are only separated by difierences in the male genital armature. These, as is 
well known, are subject to great individual variation, and why should not the characters joeculiar 
to a distinct variety, or even species, arise during the lifetime of two individuals when mated? 
An untisually vigorous polj'gamous butterfly may have some new congenital extra development 
of hooks and processes, and by frequent use develop the muscles controlling these to the extent 
of providing an acquired character, which may be, if useful, inherited in the next and succeeding 
generations. 
But an especially interesting and fruitful field of investigation would be a study of wingless 
Lepidoptera, such as the caukerworm, the autumn moths allied to it, the tussock moths (Orgyia), 
and especially the sack bearers or Psychida?. 
The loss of wings in these cases seems to be due to disuse in individuals more sluggish than 
others, and with little doubt has been the result of inheritance of Avhat were originally acquired 
characters. It is easy to imagine how this has been induced by a study of a series of forms, 
beginning with certain European genera, in which the wings of the female are very small, and 
passing to those in which they become simple pads, as in Orgyia, and ending with those such as 
Anisopteryx, in which their reduction is still further carried out. And then Lepidoptera should 
be compared with certain of the Ephemera*, whose hind wings are so much reduced; with Pezzo- 
tettix and other Orthoptera with aborted wings, and certain Hemiptera in which the wings are 
aborted, ending with the gTeat order of lliptera, comprising a vast number of species, in Avhich 
the hind wings have not only undergone a great reduction, but have been transformed through 
change of function into balancers, with their extraordinary sense organs. It is not difiicult to see 
that the disuse of wings may have begun in the life of a single individual, Avhich, losing its wings 
and having perhaps inherited a tendency to this lesion through corpulency and other bodily 
changes, became inactive, averse to flight, and finally transmitted the peculiarity to its offspring. 
In a paper in the Proceedings of the Boston Society of Natural History (xxiv, 482), on the 
life history of Drepana arcxiatay I have described the different stages of this moth, and at the end 
