2 Introduction. By Dr. A. Sisitz. 
caused by the magpie-moths and the Operoplnihera, are promoted by the extensive plantations of Ribes grossu- 
laria and of fruit-trees. 
The larvae are easily recognizable by the formation of their legs, the pupae by their slim shape, their 
smooth upper surface and their scanty web, and the imagines as a rule by a lateral cavity near the base of 
the abdomen which is easily noticed, as the body of many Geometrid species is scantily covered with hair. 
The manner of holding their wings is, on the whole, also very consistent, since a great part of Geometridae 
usually keep their wings flatly spread, when they settle for a longer rest. Wherever there are differences in 
this habit, the cause is obviously the imitation of some object of their surroundings, a withered leaf, a fruit- 
pod, or the like. 
It is also evident in most of the American Geometridae that they lack a real interior protection by poi¬ 
sonous juices. This is certainly the case in most of the species living on unpoisonous foliage. During their larval 
stage they are chiefly protected by the sheer impossibility of being recognized, and it is obvious that the 
excellent disguise as it is exhibited by a larva provided with thorns similar to those of its food-plant (e. g. the 
Ethiopian larva of Coenina dentaria Swh. living on Acacia nilotica) is hardly detected even by the eyes of 
animals. On ivy-clad one walls may readily observe the larvae of Ourapteryx, which in the daytime stick quite 
stiffly up into the air like the stalk of a leaf, remaining unnoticed even by insectivorous birds, as long as they 
do not move. On being discovered, however, they are picked off at once, and it has been ascertained by 
frequent observations that the larvae of Geometridae represent the greatest part of the food with which the 
singing-birds feed their young. 
The imagines of the Geometridae, like the larvae, try to escape the danger of being discovered by hiding. 
Owing to the resting imago’s habit of keeping its wings flatly appressed to the background, the shape of the 
insect is difficult to discern, since it is excellently concealed by the marking of dark undulating lines on the 
bark-grey ground-colour of the wings. This is particularly the case with plumper-bodied Geometrid species, 
the big bodies of which attract the insectivorous animals more than the dry, intensely dusted miniature 
bodies of the more slender Geometridae, in which the still relatively large, inedible wings form the greatest 
part of the morsel. 
The protective colouring of the Geometridae is quite general in the species which fly at night and rest 
in the daytime. Among these we also meet with most of the green lepidopteral species, since many Hemitheinae 
spend the daytime in herbs or in the foliage of bushes; besides these a very great number imitate withered or 
dry, shrivelled leaves, or white species appress themselves so closely to the underside of leaves that their glossy 
upper surface reflects the green colour of their surroundings. All these species are so well protected that they 
are only noticed when beaten off from the bushes or forced to fly away, when one kicks against young trees 
on which they have settled. The way they make use of their protective colouring is often very cunning. Thus, 
for instance, the leaves of some herbs in Brazil have been modified by coleopteral larvae (presumably Cassidae) 
to such a degree that the centre of the leaf, deprived of its epidermis, forms a hyaline spot, in which single 
chlorophyllaceous islets are still to be seen, and which strongly contrasts with the broad green edge of the 
leaf. On the same vegetable species, exhibiting such half-skeletonized leaves, a Geometrid species, Trygodes 
musivaria , settles on the leaves in such a way that the lepidopteron represents the skeletonized patch, whilst 
the edge of the leaf representing the apparently undamaged part projects on all sides in the same width. 
The insect mostly places so much confidence in this disguise that it only flies away on being touched. 
The fact that other Geometridae have adapted themselves to the bare soil, or to places in wood stripped 
of the bark, or to twigs or leaves soiled by birds’ droppings, or to the rocky subsoil, to walls or planks, has 
been proved by many examples in all the faunistic regions of the earth, and especially in America. We can 
always ascertain that also the attitude of the lepidoptera exactly corresponds to the colour of the surround¬ 
ings to which it has adapted itself. Many Microgonia exhibit the well-known oblique stripe extending from 
the apex across the centre of the inner margin of both the fore wings to the other apex, corresponding to the 
midrib of the mimicked leaf. The imago is very rarely discovered in this resting position; it then sits on a 
dry tendril or a loose petiole in such a way that the apex of the one wing usually also exhibiting a small 
stalk-like tip lies flat against a stalk where the leaf might have grown, whilst the apex of the other forewing 
extends into the air like the apex of the leaf. 
All these qualities, especially the extremely minute adaptation, the developement of which must 
surely have taken ages, and besides the universal distribution extending even across the geologically oldest 
countries — the Geometridae predominate in such countries as New Zealand and Australia —, their habits 
being mostly nocturnal, averse to the sun, the inflexibility and a certain monotony of their exterior, — all 
these facts seem to prove that the Geometridae are a very old lepidopteral tribe. Moreover, the vast range of 
some species (e. g. Calocalpe undulata L.) often extending, as we mentioned above, across all the continents 
of a hemisphere, the frequent reoccurence of particularly grotesque forms in distantly remote countries, as 
for instance the vermicularly prolonged body with reduced hindwings in New Zealand (Tatosoma agrionata 
