290 PACKARD — OPISTHENOGENESIS. [June 15, 



of this mode of origin of the markings as the '' law of wave-like 

 evolution, or law of undulation." In confirmation of this process 

 or law he cites the conclusions of Wurtenberger/ who had long 

 before (1873) observed that in ammonites all structural changes 

 show themselves first on the last (the outer) whorl of the shell, such 

 a change in the following generations being pushed farther and 

 farther towards the beginning of the spiral, until it prevails in the 

 greater number of the whorls." 



Cope, in his Primary Factors of Organic Evolution (1896), also 

 shows that in the lizards Cnemidophoriis tesselatus and gularis the 

 breaking up of the striped coloration into transverse spots begins 

 first at the sacral and lumbar regions: ''The confluence of the 

 spots appears there first." 



We may cite some examples of this law of growth a tergo, or 

 opisthenogenesis, as it might be called, which have fallen under our 

 own observation.^ 



In Dasylophia ajtguina, as shown by the figures in Plate XXI ot 

 my monograph of the bombycine Moths, Pt. i, it will be observed 

 that in stages III, IV and the last stage the dark longitudinal 

 lines become on the eighth to tenth abdominal segments broken up 

 into separate isolated dark spots. In the larva, before the second 

 molt, there are no spots on the ninth and tenth segments. In stage 

 III, however, i.e., after the second change of skin, as stated in my 

 monograph (p. 175), four black spots now appear on the front part 

 of the suranal plate. In the last stage, the reddish spots on the 

 eighth abdominal segment which are detached from the lateral 

 lines of stages I and II, now become specialized into the two black 

 comma-like spots, with a linear spot above and beneath ; the two, 

 sometimes divided into four, black spots arise on the suranal plate. 



It thus appears that in the ontogeny of this species the process of 

 breaking up or origin of the spots from the longitudinal lines takes 

 place on the last three segments of the body. 



In Symmerista albifrons the same phenomenon occurs. In stage 

 I, as stated in my monograph (p. 180), on each side of the ninth 

 segment is a large black comma-shaped spot, the point directed 

 forward and downward, while behind there is a median black dot. 



1 A New Contribution to the Zoological Proof of the Darwinian Theory, 

 Ausland, 1873, Nos. I, 2, and Studies on the History of the Descent of the 

 A??inionites, Leipzig, 1880 (in German). 



2 Froc. Amer. Asso. Advancement Science, Boston Meeting, 1898, pp. 368-9. 



