192 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



glaucous blue, salmon-buff, 6cru-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 America display but 36 colors, while 22 

 in Xorth America 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 Tropics than in the Temperate Zones, so that the Trop- 

 kal species must possess a correspondingly greater opportunity to 

 vary. 



Y. The Causes which have led to the Development an'd 

 Preservation of the Scales of the Lepidoptera. 



(1) i:.qieriments and 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 

 bodj-surface of most Arthropods, up to perfectly 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 Avith 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 cell of the hypodermis, which Hes below the 

 cuticula. They have probably been developed because the cuticala. 



