192 BULLETIN: MUSEUM OF COMPARATIVE ZOÓLOGY. 
glaucous blue, salmon-buff, écru-drab, flesh-color, coral-red, rose-red, 
vermilion, rufous, geranium-red, geranium-pink, olive-buff, iridescent 
geranium-pink (as in P. zeuxis), and transparent areas. 
As 200 species in South Americ: display but 36 colors, while 22 
in North Ameriea show 17, it follows that, while the number of 
species in South America is 9 times as great as in North America, 
the number of colors displayed is only a little more than twice as great. 
The richer display of colors in the Tropics, therefore, may be due 
simply to the far greater number of species, which gives a better oppor- 
tunity for color-sports to arise, and not to any direct influence of the 
climate. The number of broods, also, which occur in a year is much 
greater in the Tropies than in the Temperate Zones, so that the Trop- 
ical species must possess a correspondingly greater opportunity to 
vary. 
V. Tue CAUSES WHICH HAVE LED TO THE DEVELOPMENT AND 
PRESERVATION OF THE SCALES OF THE LEPIDOPTERA. 
(1) Experiments und Theory. It is well known that the scales 
of Lepidoptera are morphologically identical with hairs. Indeed, a 
graded series from simple hairs such as are found covering the 
body-surface of most Arthropods, up to perfeetly developed flat 
scales bearing well differentiated striae may usually be found upon 
one and the same insect. 
It is also remarkable that the color-bearing scales of beetles have 
been developed in the same manner as those of moths and butterflies, 
and that in this case also hairs have become differentiated into scales 
which are precisely similar in appearance to those of the Lepidoptera 
(see Dimmock, ’83). 
This is only another of the numerous instances met with in nature 
where similar conditions of selection have developed complex organs 
which are similar in appearance, though found in widely separated 
groups. A list of papers relating to the development of scales has 
been given by Dimmock (83, p. 1-11). 
Most of the hairs which cover the body-surface in Arthropods are 
true sensory structures, the axis of each of which is a protoplasmic 
process from a single eell of the hypodermis, which lies below the 
cuticula. They have probably been developed because the cuticula, 
