1890.] 
503 
[Packard. 
placed on a sound basis the theory of the origin of the lines, bands 
and spots of the Sphingidse. The additional notes by Professor 
Meldola, and the beautiful researches of Mr. Poulton, have added 
to the strength of the arguments of Weismann. The lines, bars, 
stripes, spots, and other colorational markings of caterpillars, by 
which they mimic the colors and shadows of leaves, stems, etc., 
have evidently been in the first place induced by the nature of the 
food (chlorophyll), by the effects produced by light and shade, by 
adaptation to the form of the edge of the leaf, as in the serrated 
back of certain Notodontians, by adaptation to the colors of dif- 
ferent leaves and to the stems, often reddish ; shades of greens, yel- 
lows, reds, and browns being as common in the cuticle of cater- 
pillars as on the surface or cuticle of the leaves and their stems, or 
in the bark of the twigs and branches. We (and probably others) 
have observed that the peculiar brown spots and patches of certain 
Notodontians do not appear until late in larval life, and also late 
in the summer or early in the autumn contemporaneous with the ap- 
pearance of dead and sere blotches in the leaves themselves. 
Now to say that these wonderful adaptations and marked changes 
in the markings of caterpillars are due to “ natural selection,” and 
to let the matter rest there, is quite unsatisfactory. Natural selec- 
tion may account for the elaboration of these larval forms with 
their markings after they have once appeared, but we want to dis- 
cover, if possible, the original causes of such ornamentation, i. e., 
the primary factors concerned in their evolution. Weismann, in 
his earlier work, repeatedly asserts that these changes are due to 
the direct action of external conditions together with natural selec- 
tion. Within a few years past many naturalists have returned to 
a more profound study of the causes of variation along some of the 
lines vaguely pointed out by Lamarck 1 . It is noteworthy that 
Herbert Spencer says : “ The direct action of the medium was the primordial factor 
of organic evolution.” (See The Factors of Organic Evolution, 1886.) Claude Bernard 
wrote: “The conditions of life are neither in the organism, nor in its external sur- 
roundings, but in both at once.” (Quoted from J. A. Thompson’s Synthetic Summary of 
the influence of the environment upon the organism, Proc. Roy. Phys. Soc., ix, 1888.; 
Sachs remarks: “A far greater portion of the phenomena of life are [is] called forth by 
external influences than one formerly ventured to assume ” (Phys. of Plants, 1887, 191, 
English translation). Semper claims “that of all the properties of the animal organism, 
variability is that which may first and most easily be traced by exact investigation to 
its efficient causes” (Animal Life, etc., preface, Vi). “External conditions can exert 
not only a very powerful selective influence, but a transforming one as well, although 
it must be the more limited of the two ” (lb., 37). “No power which is able to act 
only as a selective, and not as a transforming influence, can ever be exclusively put 
forward as the proper efficient cause — causa efficiens — of any phenomenon (lb. 404). 
