KELLOGO: TAXONOMIC VALUE OF SCALES OF LEPIDOPTERA. 79 



shrill sound, as otherwise occurs in the male of Thecophora fovea and 

 in the male of the Indian Caristes jnembranacea. Scudder (Butter- 

 flies of the Eastern United States and Canada) has heard Vanessa 

 antiopa make a grating sound while fanning its wings together, and 

 he artificially produced this sound after the death of the butterfly by 

 rubbing the wings together. Inachis to and Parnassius apollo have 

 been heard to make sounds while moving the wings, presumably 

 scraping them together. 



V. 



In the light of the observations just recorded on the structure, 

 functions and development of the scales of Lepidoptera, we may 

 reasonably attempt to derive from the conditions of the scales in 

 various lepidopterous species and groups, the testimony which the 

 scales bear as to the phylogeny of lepidopterous forms. In a word, 

 we may attend to the taxonomic value of the scales. 



The characters possessed of taxonomic value, or value of the char- 

 acters for the classification of the organisms, are not merely those 

 characters by which one species or group of species may be recog- 

 nized at glance to be different from other species, but, more truly, are 

 characters which indicate lines of specialization and thus lines of 

 descent, i. e., phylogenetic relationships.* 



Any organ of the insect body has reached its present condition only 

 by gradual and constant specialization. This specialization may be in 

 the nature of an additional development of the organ so that it may 

 more effectually perform its function, and usually is; as in the special- 

 ization of a weak, flexible hair to a strong, flat scale, the function being 

 that of strengthening a delicate membrane. Or the specialization 

 may be in the nature of a degradation or retrogression of the organ 

 by reason of a doing away with the need of the functions of the 

 organ, and consequently with the need of the organ itself. 



Or the organ may be thus degraded when its function is performed 

 by a substitute for it; or when its function is of less importance, 

 less advantage, than some other condition or need which would be 

 impaired by the presence of the organ. This latter case is exempli- 

 fied in the retrogression and fading out of the scales from the clear 

 areas of the Sesiid?e and other similarly mimicking Lepidoptera. 



The various functions, also, fulfilled by scales, render the inter- 

 pretation of their phylogenetic significance the more difficult, as the 

 state of specialization may depend now on the value of one function 

 and now on another. Practically, in considering the scales, but two 

 functions are thus complicated, namely, those of strengthening the 



a discussion of t'ae sigiiifieauce of cliaracters, see p. 61. 



