Introduction. By Dr. A. Seitz. 
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Wile.) and then again in Chile (Pachrophylla linearia Blanch.), and many other facts likewise arc in favour 
of the assumption that the Geometridae. belong to a palaeontological branch of the lepidopteral tribe. But as 
is frequently the case in the animal kingdom, single offshoots of this tribe seem to have adapted themselves 
to the modern times and to have gone on developing themseles into sun-loving, variegated diurnal lepidoptera 
which often exhibit a magnificent metallic exterior. As the Dysphania and Milionia in the Indian fauna 
and the Aletis in Africa, so the Nelo, Siosta, Sangalopsis, and Devarodes in America preferably fly about in 
the brightest sunshine in open spaces, taking up water from puddles in the roads, and moving about most 
conspicuously, evidently unmolested by insectivorous animals. It seems that some interior protection has 
developed itself also in the day-flying, glaringly yellow Gyllopoda in the same way as in the palaearctic Abraxas, 
for, as in the European Abraxas grossulariata, the larva of Gyllopoda, contrary to nearly all the Geometrid 
larvae, exhibits variegated spots behind the head and at the anal end, and has also diurnal habits; it has 
ceased to show resemblance to a twig, but has a stout, cylindrically shaped body. This diurnal life in the sun 
is a preliminary condition for the development of mimetic assimilation, and although cases of minute mimicry 
only occur very exceptionally in the Geometridae, yet resemblances to notoriously protected butterflies are 
to be noticed in certain groups. Thus, for instance, there are the most conspicuous Siosta bifasciata Lair, in 
the west of Tropical America, and at the very same place we find the likewise black Actinote (larva on Solaneae) 
exhibiting a scarlet mark at the same place on the wing and so offering the same exterior as the Geometrid 
form flying among them; even colours entirely uncommon in Geometridae, as the black vestiture of the Peru¬ 
vian Actinote anaxo Hpff., recurs in the Peruvian Geometrid Siosta. 
Other Geometridae seem to have only lately commenced with a certain adaptation to their surroundings, 
and the resemblance has not yet passed beyond the stage of a rough beginning. Thus we find among the 
Erycinidae of Tropical South America the widely distributed genus Ancyluris exhibiting a peculiar distortion 
of the hindwings, the anal parts of which are extended to broad, lobate tails with a reddish-yellow, red, or 
white marking on a deep black ground (cf. Vol. V, pi. 129, 130). At the same place as these Ancyluris fly 
the Geometrids of the genus Erateina exhibiting the same contortion of the hindwings which, as in the 
Ancyluris, have the shape of a broad stripe ending in a lobate tip and are likewise decorated with orange, 
yellow, or red on a dark ground. This shape, however, is produced in an entirely different, somewhat violent 
manner: i. e. so much of the inner-marginal portion of the hindwing being turned under in the <$$ of these 
Geometridae, that the part of the wing which is visible from above shows exactly the shape of the hindwing 
of Ancyluris. It is a curious fact that this reversed inner-marginal lobe does not exhibit the marking of the 
upperside to which this surface really belongs, but forms an exact continuation of the most complicated 
marking of the hindwing beneath, so that the scheme of colouring and marking appears to be almost turned over. 
If we examine the pouch produced thereby at the inner margin of the hindwing, which we find particu¬ 
larly well developed in the of Erateina undulata Saund., it proves to be densely filled with an accumulation 
of modified scales which have not only lost their colouring altogether, but also have undergone a change in 
shape, as it frequently reoccurs in the so-called scent-organs of certain lepidoptera. All the terminal teeth of 
the scales have vanished and been transformed to oblong-oval scales or awl-shaped formations which are 
sometimes joined together like copulating Gregarinae. 
In general, distinct scent-organs rarely occur in the other Geometridae. The forewings of some American 
Larentiinae sometimes show comb-shaped strigiform pads — for instance in the Peruvian Obila gibbosaria —, 
or accumulations of scales projecting from the costal margin, as in Obila floccosaria Walk. On examining the 
curls of hair under the microscope they prove to be composed of wing-scales having grown into long hairs 
that have become long, somewhat undulated threads in 0 . gibbosaria, whilst those of 0 . floccosaria show a 
widening at the end, where we still notice traces of the terminal teeth of the scales. In most of the groups, 
however, the scaling does not differ considerably from the usual shape of the other lepidopteral families. 
The size of the wing-span of the American Geometridae is certainly not inferior to the extreme sizes 
of those of other faunae, though it does not exceed them. The largest American Geometridae are probably the 
females of certain Microgonia, such as M. guenei Warr. with an expanse of 8—9 cm, similar to that of the 
Indo-Australian Medasina, Xandrames, Elphos, or Erebomorpha. Thus the American Geometridae do not show 
a superiority over all the other Geometridae as the South-American Noctuid Thysania agrippina does over 
all the other Noctuids. Moreover, there occur very small Sterrhinae in America, but they only form a parallel 
to the diminutive size of numerous palaearctic forms, such as the European Ptycliopoda nexata Hbn., the 
Asiatic Ptych. nielseni Pled., or diminutive African Hemitheinae. Among the very smallest Geometridae of 
America numbers also the peculiar species Sterrha bonitata Hist., the ill-famed devastator of the herbaria, the 
larva of which does not even attain a length of 1 cm. 
As is the case in the members of other lepidopteral families, the size which the Geometridae may attain 
is not proportionate to the frequently luxuriant abundance of food. The limitation of size, however, seems 
to be rather due to their mode of moving. The high arch formed by the dorsum of the moving larva cannot 
