Packard.] 
512 
[Feb. 19, 
these factors are all-important in the evolution of the colors, orna- 
ments and outgrowths from the cuticle of caterpillars . 1 
The following table is an attempt at a classification of some of 
the structures arising from the various modifications of the primi- 
tive piliferous warts or tubercles common to nearly all, if not all, 
smooth-bodied, lepidopterous larvae. As is well known, the term 
“ hair” does not properly apply to the bristles or hair-like struct- 
ures of worms and Arthropoda, as morphologically they are not 
the homologues of the hairs of mammals, but arise, as Newport 
first showed, through a modification and hypertrophy of the nuclei 
of certain cells of the cuticle. Hence the word seta , as suggested 
by Lankester, is most applicable. 
A. Tubercles. 
a. Simple and minute , due to a slight thickening of the hypodermis and 
a decided thickening of the overlying cuticle ; the hypodermis contains a 
large unicellular gland either for the secretion of the seta (or for the pro- 
duction of poison). 
1. Minute piliferous warts. (MostTineid, Tortricid andNoctuid larvae.) 
2. Enlarged smooth tubercles, bearing a single seta. (Many Geometrid 
and Bombycine larvae.) 
3. Enlarged, spherical tubercles, bearing a number of setae, either radi- 
ated or subverticillate. (Arctians, Lithosians, Zygaenidae, including 
some Glaucopinae.) 
4. High, movable, smooth tubercles, having a terrifying function. ( Schi - 
sura , Janassa , Notodonta , Nerice.) 
5. Low and broad, rudimentary, replacing the “ caudal horn.” (Choero- 
campa, the European Pheosia dictcea and dictceoides .) 
b. More or less spinulose or spiny (disappearing in some Sphinges after 
stage I). 
1. Long and slender, usually situated on top of the eighth abdominal 
segment, with microscopic spinules in stage I. (Most Sphingidae and 
Sesia .) 
1 It is possible that the close resemblance of the warts, projections and spines of cer- 
tain arboreal caterpillars, which^so closely mimic the spines, leaf-scars and projections 
of the branches or twigs or plants, has been brought about in a way analogous to the 
production of spots and lines on the body of caterpillars. Darwinians attribute this to 
the action of “ protective mimicry,” but this expression rather expresses the result of 
a series of causes to which we have endeavored to call attention. The effect of dark 
and light shades, and the light and shade in producing the stripes and bars of caterpil- 
lars are comparatively direct and manifest, but how can thorns and other projections 
on trees and shrubs affect caterpillars directly ? Given the origination by hypertrophy 
of warts and spines, and it is then easy to see that by natural selection caterpillars may 
have finally become adapted so as to mimic similar vegetable growths. Our object is 
to endeavor to explain the causes of the primary growth and development of such 
projections, i. e., to lay the foundation for the action of natural selection. 
