:\IEMOIKS OF THE NATIONAL ACADEMY OF SCIENCES. 9 



is like scvcM'iil cif the otliof species, yoUowi-^h. with twin rc<l(lisli lonn-itudinal stii|)('s. Al'lcr tho 

 third molt ;i yi-oal (liaiisie in the clmi'iictcr of th(> niariiinys laivcs place 'I'lic lono-itudinal stripes 

 now (lark or blackish brown and the yellowish or whitish stripes l)et\v(>eii them are so broken up 

 that the result is a series of transverse lines of spots of those colors. As stated l)y Doctor Dyar, 

 who has reared the insect from the eyo- antl allowed me to publish his notes in my mouooraph, Pt. I 

 (p. 114). the lin(>s are broken by the l)lack i^round color into a series of s(|uarish spots. "'The 

 two upper lines are liroken in all the segmental incisures an<l broadly thi'ouu'h the center of the 

 segment; the third (lateral) is brok(Mi in the same manner, but less broadly in the center of the 

 segment, while the fourth (substigmatal) is not liroken in the incisure nor center of the segment, 

 but once befoi-e the spiracle and again toward the posterior edge of the segment." 



It will readily be seen that in the course of its ontogeny Datana jiuijcr passes thi-ough the 

 stages of coloration and markings of all the other species whose postembryonic development is 

 known, i. e., recapitulates their phases of coloration, but finally pushes back these phases in the 

 ontogeny and enters upon a more ad\anced stage, showing that it is phylogenetically the young- 

 est of all our species of Datana. 



How far successful thi' new style of markings thus obtained is over that of the older, more 

 primitive species remains to be seen when further observations on this rather rare species shall 

 enable us to see how well it is protected, either by its markings or its bad taste. 



Further observations are needed in order to ascertain whether the process of breaking up of 

 the longitudinal stripes into transversely arranged spots began at the hinder end of the bod\'. 

 The fact that the process began from above, where a greater amount of light falls upon the body, 

 resulting in white or yellow spots on a black ground, would seem to be an exemplification of 

 Thayer's law; that "animals are painted by nature darkest on those parts which tend to be most 

 lighted by the sky's light."" Again he says: "• While nature undeniably completes the conceal- 

 ment of animals by pitching their whole color gradation in a kev to match their environment, 

 the real magic lies in the gradation itself from darkest above to lightest below wherever this 

 gradation is found." 



PHYTOGENY OF THE SPECIES OF DATANA. 



Of the twelve known species or forms of this genus only a single one appears to have under- 

 gone in the larval state a high degree of specialization of its markings, i. e., the transformation 

 of the longitudinal stripes into transverse sei'ies of bright conspicuous whitish or yellowish 

 spots, such as occurs in the ontogeny of D. nmjor. 



Since this radical change in the style of markings does not take place until after the last 

 ecdysis, the species has evidently only recently evolved; it is phylogeneticalh' the youngest 

 species of the genus. We thus have in our hands a means of classifying the species of the genus, 

 or at least of dividing them into two groups, i. e., comprising those which retain their stripes 

 throughout larval life, and the single one (unless additional species should occur) in Avhich the 

 body is transversely spotted. 



Since the number of species in this genus is large, and the individuals abound, the type was 

 evidenth' a verj' successful one, and how successful the spotted species is, being so far as known 

 rather rare, and how much it is aided by its spotted coat in evading the attacks of birds, etc., in 

 the struggle for existence would be an interesting inquiry. 



The genus Datana and its European ally Pygara are members of a distinct subfamil3-, which 

 has originated in the arctogaeic area, and as the .species of Datana are confined to America 

 north of southern Jlexico, and within that region are unusuallv numerous, both in species and 

 individuals, it is to be presumed that the original point of origin of the subfamilj^ was on the 

 Atlantic side of the North American continent. If this be the case the two Eurasian species of 

 Pygsera may be the descendants of late Tertiary emigrants from the polar regions. 



"The law which underlies protective coloration. Smithsonian Report for 1897, p. 477. 



