8 
MEMOmS or THE NATIOiTAL ACADEMY OF SCIEKOES. 
4. To obtain facts regarding the ontogeny of our native species and genera wbicli, when added 
to what we know of the life histories of Europea]), Asiatic, and Soiitb American Bombyces, may 
lead to at least a partial comprehension of the i)hylogeny of the higher Lei^idoptera, viz, those 
above tbe so-called Microlei>idoptera. 
The transformations of the Bombycine moths are especially noteworthy and useful for the 
purposes Ave have indicated, since the group is rich in stem forms, because of its probable 
geological antiquity, and because of the remarkable and significant differences i)resented by the 
larvic of many of the groups in the numerous successive stages of their larval life, these stages 
being characterized by distinctive and highly modified shapes, colot^s, markings, and armatimes. 
These peculiarities, signalizing nearly each stage, were, we believe, evolved in direct response 
to the changes in their environment, in their mode of life, or to changes in their food plants, 
and the necessity of being protected through unconscious mimicry from the assaults of insects and 
reptilian and avian enemies. 
The transformations also afford the clearest i:)ossible evidence of the action of AAhat Darwin 
calls “inheritance at corresponding periods of life,” and which Ilmckel has tersely designated as 
“homochronic heredity.” 
This fact, moreover, of inheritance at corresponding periods of life throws light on the 
problem so much under discussion at the present day of the transmission of characters acquired 
at different epochs during the life of the individual. We have devoted a section to a discussion 
of this question, or rather to a review of some of the facts which strongly suggest the truth of 
this principle. 
The characters, so unexpected and striking, as for those worked out in Heierocampa hiunilata^ 
H. guttivitta, and ohliqiia, for example, as well as numerous other of the ^otodontiaus and allied 
families, are idainly enough useless to the insect in the pupa or imago condition, and have evidently 
been inherited as the result of impressions or stimuli received from without at different periods in 
the life of the caterpillar alone. 
Such cases occur in many other Arthropods, especially in the barnacles, and in the Decai^oda,. 
as well as in the parasitic worms, but the causes can nearly as well be investigated in these insects, 
which are so accessible. 
Another series of problems is opened up by a study of the mouth-parts of the Bombyces and 
of their venation, which disclose facts intimately bearing on the genealogy of the Lepidoptera. 
, In no other Lepidoptera has the agency of use and disuse, particularly the latter, been more 
marked. While the mandibles are present in certain of the Tinema and Fgralklinaj they have 
totally disappeared from the so-called Macrolepidoptera, or higher and less generalized and primi- 
tive groups. In the Bombyces, particularly the Saturnians, the maxilhe, owing to disuse, have 
undergone great reduction, with complete loss of their original function. In another direction, 
i. e., in the veins of the wings, there has been a reduction in their number, and this is correlated 
with their loss of power of taking food, the great but weak wings of these colossal moths being of 
no use in seeking for food, which they do not need; as, unlike the swift visitors of dowei\s, the 
butterflies, Sphinges, and l!loctuids, they are too feeble of flight to sip the nectar of flowers, or 
too short lived to need any nourishment. 
The geograj»hi(;al distribution of the Bombyces also tends to confirm the view that they are 
an ancient and generalized group, and to this subject we have given special attention. 
In the systematic portion of the work I have endeavored to arrange the families, genera, and 
even the species, in accordance with the probable phylogeny of the group. I have begun my 
account of the entire superfiuuily with what I regard as the most primitive family. The seven 
subfamilies of i^otodoiitiaus easily fall into this arrangement; it is not difficult to lAerceive that 
the Gluphisiinm and Dataninm are the most generalized, and that the Cerurinm are the most spec- 
ialized, whether we study the larvm or imagines, though much the clearest light of course is thrown 
upon the subject by thelarvm. It is less easy to indicate the true succession of the genera, though 
the way is made very plain in the subfamily of IIeterocampiua\ 
The proper sequence of the species in a large genus is always difficult to make out. It is 
obvious, however, that the old, unphilosophic method of designating such and such a species as the 
type of a genus, and then arranging all the others under it, is a thoughtless procedure. Usually 
