May 28, 1885] 
quotes many instances in which the larva of S. /jgustri has been 
observed to vary according to its food-plant (laurustinus, lilac, 
privet, ash). I have for many years known of the difference 
between the lilac and privet forms (the latter being of a brighter 
yellower green than the former, with brighter stripes). In 1884. 
I bred twelve larvee from the egg upon privet, and the same 
number upon lilac. All the privet and six of the lilac larve 
reached maturity, and, without exception, showed the differences 
indicated above. A more remarkable instance is afforded by 
Smerinthus ocellatus. Mr. Meldola quotes Mr. E. Boscher as 
finding many yellowish-green varieties of this larva upon Salix 
ziminalis, and many bluish-green varieties upon S. ¢viandra, 
similar to those which are well known to occur upon apple. 
The former yarieties possessed the rows of reddish-brown spots 
which sometimes occur on this variety of the larva. Upon 
another species of Salix he found instances of both varieties. In 
1880 Mr. Boscher conducted some breeding experiments at Mr. 
Meldola’s suggestion, feeding the larve from the ege upon 
S. triandra, S. viminalis, and apple, respectively. Only three 
of the third lot survived, and were all of the bluish-green form. 
I have also found (77ams. Ent, Soc., Part I., April, 1884) that 
S. rubra and S, cinerea produce the yellowish variety, but 
S. viminalis the bluish form, according to my experience. In 
1884 I fed five lots of six larvee each, from the egg, upon apple, 
crab, Salix viminalis, S. cinerea, and S. rubra, respectively. 
On a few occasions S. dadylonica and ¢riandra were substituted 
for S. rubra, and ordinary apple for crab. The eggs were 
hatched July 15 to 18, and most of the larvze were full fed by 
August 23, with the following results :—4///e: the five larva 
were typical bluish-green forms. C7aé: the five larvae were 
also typical bluish-green. S. vzmznalis: the four larvzee were 
not so whitish as the above-mentioned lots, but were almost 
intermediate. S. cinerea: the four larva were also intermediate. 
S. rubra; the four larvee were yellower than any of the others, 
but were not much beyond intermediate forms. The yellowest 
was separated on August 14, and fed upon apple, becoming 
adult August 26, by which time it was rather whiter than any 
others of the same lot (S$. rubra). 
Thus there was no doubt about the effects produced, but there 
was a strong tendency all through towards the bluish variety, 
which the food-plant could only overcome to the extent of 
producing an intermediate form. The same conclusions were 
formed by a comparison of larvee found in the field during 1884. 
Thus two nearly opposite varieties were found upon the same 
tree (? S. ferruginea, Anderson); an intermediate variety was 
found upon S. rxéra, and a bright yellowish variety upon apple. 
At the same time the great majority of larvze found were such as 
I should have anticipated. 
Experiments were made upon the younger captured larve, 
which were fed upon food-plants tending towards a different 
colour. The results were similar to those indicated by the 
former experiments. Some effect could be produced in an 
intermediate variety by feeding it for some considerable time 
upon a food-plant known to have strong tendencies, but no 
such effect is produced upon a larva with a strongly-marked 
colour, z.e. one with strong tendencies itself, and corresponding 
with those of the food-plant. But the former experiments show 
that a very strong larval tendency may be counteracted to the 
extent of producing an intermediate form by feeding it from the 
egg upon a food-plant tending strongly in the other direction. 
When this latter effect has become manifest, it was proved that 
an appropriate change of the food at a comparatively late period 
may produce some considerable effect in the direction of the 
original tendency. The most probable explanation of the above- 
mentioned facts is that the effects of the food-plant are here- 
ditary, and accumulate when the larvze of successive generations 
feed upon plants with the same tendencies. Conversely feeding 
upon plants with different tendencies, and interbreeding, ac- 
counts for the irregularities observed. Thus in the larve fed 
from the egg, it is supposed that the previous generation (or 
generations) fed upon plants tending towards bluish-green larvze. 
The yellowish larva found upon apple must have descended 
from a line fed upon S. vuéra, or a plant with the same effects. 
The localisation of a food-plant would overcome both causes of 
irregularity, the liability to lay eggs on plants with different 
tendencies, and the chance of interbreeding between the two 
varieties. 
This explanation is in accordance with the fact that the larvee 
are of a very uniform tint upon apple trees in gardens, which 
are to a certain extent locally separated from the various species 
NATURE 
ot sallow growing by the banks of streams, and in damp lanes and 
hedgerows. The strong effects produced upon the larvae by 
apple, the usual proximity of many trees, and the sluggish flight 
of the Smerinthi, doubtless all conduce towards the uniformity 
between the larvae upon this food-plant. On the other hand, 
there is the greatest facility for (the observed) irregularity in the 
results of sallow upon the larvze, for many so-called species with 
various tendencies grow close together, so that there must be 
interbreeding and the deposition of eggs on various species of 
food-plants, even in the case of very sluggish insects. It is 
probable that certain conflicting statements as to the effect of 
the different food-plants upon the larva of S. Zigustri are to be 
explained in the same way. As to the structural cause of the 
variability in these two larve, the main factor is a change in the 
relative amounts of the two derived pigments. Thus there is 
more xanthophyll in the blood of the pupa of a yellowish 
S. ocellatus than in the other case ; and more chlcrophyll with 
less xanthophyll, in the blood of the pupa of S. Zgustri, from 
the greener larva fed upon lilac than from one fed upon 
privet. The result of this adjustment of the relative 
amounts of derived pigment is to produce a colour which har- 
monises with the part of the environment imitated—the under- 
sides of the leaves in the case of S. oce//atus, the tout ensemble of 
the food-plant in the case of S. /igustr?. In neither instance 
can the effects be due to the most direct and simple action of the 
food itself—the solution of its pigments in their normal propor- 
tion showing through the skin. This is disproved by the fact that 
S. ocellatus eats the whole leaf, but resembles the underside, 
and imitates in derived pigments an appearance largely due to 
texture ; further, the effects do not at once follow a change of 
food, and a strong larval tendency may even cause the re- 
arrangement of the derived pigments, so as to produce an effect 
unlike the leaf. The simple view allows no room for larval 
tendencies or for delayed effects. It has also been rendered 
very probable that the effects accumulate during successive 
generations. In the case of S. ligustri there is the additional 
difficulty that the larval pigment of the oblique stripes is affected 
by the food-plant as well as the derived pigments. Such effects 
cannot be explained by any simple theory of phytophagic effects, 
but it still holds good that phytophagic pigments play a most im- 
portant part in larval coloration, and afford the chief material 
whichis moulded by some influence—subtler than that which is im- 
plied by the term ‘“‘phytophagic” itself—into likeness to a special 
part of the environment. The little we know of this influence 
points towards a nervous circle whose efferent effects are seen in 
the regulation of the passage of altered plant-pigments through 
the digestive tract into the blood, and finally the tissues, and in 
the colour of a certain amount of larval pigment, while the 
afferent part of the circuit must originate in some surface capable 
of responding to delicate shades of difference in the colour of the 
part of the environment imitated This interpretation is rendered 
unusually difficult by three facts : the gradual working of the pro- 
cess, often incomplete in a single life ; the excessively complex and 
diverse results, and the special character of the stimulus (for it is 
only the part of the environment imitated which produces any effect 
—e.g. the undersides only of the leaves in the case of S. oce//atus). 
During the present year I hope to experiment further upon the 
subject, and I have a large number of living pupe of S. 
ocellatus, with the life-histories of their respective larve care- 
fully noted 
Chemical Society, May 7.—Dr. Hugo Miiller, F.R.S., 
President, in the chair.—The following papers were read :—On 
some points in the composition of soils ; with results illustrating 
the sources of fertility of Manitoba prairie soils, by Sir J. B. 
Lawes, Bart., LL.D., F.R.S., F.C.S., and J. H. Gilbert, 
Ph.D., LL.D., F.R.S., V.P.C.S.—Researches on the relation 
between the molecular structure of carbon compounds and their 
absorption spectra, by Prof. W. N. Hartley, F.R.S. In con- 
tinuation of the author’s previous researches (Z7avs., 1881, 
57-60 and 111-128; 1883, 676-678), measurements have been 
made of the wave-lengths of the rays absorbed by the following 
substances :—(1) Aromatic hydrocarbons: benzene, the three 
xylenes, and naphthalene. (2) Aromatic tertiary bases and 
their salts: pyridine, picoline, quinoline, and their hydrochlor- 
ides. (3) Addition products of tertiary bases and salts: piper- 
idine, tetrahydroquinoline, and its shydrochloride. (4) Primary 
aromatic bases or amido-derivatives and salts thereoi: ortho- 
and para-toluidine and their hydrochlorides. In the preparation 
of solutions, a milligram-molecule, that is, the molecular weight 
