PHYCIODES I., II. 



chrysalis apparently comes out of, in precisely the same condition as it went 

 into, its cold bath. Nevertheless, during the subjection to cold, some change 

 has taken place, by which the coloration of one of two dimorphic forms of 

 the butterfly has been made to appear rather than the other. 



As to the degree of cold necessary to effect a change of form, it need not be 

 extreme, or so low as the freezing point. The most successful changes, with lit- 

 tle loss of life, have been eflected when the temperature was about 40°. The 

 steady coolness of the natural temperature on the last chrysalids at Hunter, in 

 1876, effected a complete change of form. A freezing temperature has resulted 

 in the running of the colors to a considerable extent, and a few butterflies 

 changed without suffusion, but the loss was very heavy. In 1878, I placed 

 twenty-six chrysalids of Grapta Inierrorjatioms on ice, keeping them at 32°j for 

 an average period of fifteen days, and every one was destroyed. At the same 

 time, however, chrysalids of Ajax were in the box, and most of them survived 

 the exposure, though up to the date of this writing, now forty-one days after 

 they were removed from the ice, only three butterflies have emerged. One of 

 these was exposed in chrysalis at full three days after forming, and is changed to 

 Telamonides ; and the other two, exposed at less than twelve hours after form- 

 ing, are Walshii in markings, with the shape of 3farce^us. 



Of the four principal varieties of the winter form of Tharos, A appears to be 

 an offset of B, in the direction most remote from the summer form, just as 

 Walshii is on the further side of Telamonides, remote from the summer form 

 Marcellus. On the contrary, C leads from B through D, directly to the sum- 

 mer form. Var. B may be nearest the primitive type of the species. Be- 

 sides that this has appeared constantly in the butterflies changed by cold, it 

 predominates in this region over the other varieties. Moreover, its distinctive 

 peculiarity of color is seen in the nearly allied species Phaon and Vesta, both 

 which are seasonally dimorphic, and seem to be restricted in their winter forms 

 to the single phase denoted by B in 3Iarcia. And in their summer generations 

 both these species have a close resemblance to the summer Tharos, even to 

 the peculiar variety C of this foi'm, which is found in all three. It is notice- 

 able that these three species should be seasonally dimorphic, with the forms so 

 resembling each other, while the other species of Phyciodes inhabiting the Atlan- 

 tic slope show no especial difference between their winter and summer genera- 

 tions. 



The significance of these phenomena I take to be this : when Phaon and Vesta 

 and Tharos were as yet only varieties of one species, the sole coloration was sim- 

 ilar to that now common to the three. As they gradually became permanent, or 

 in other words, as these varieties became species, Tharos was giving rise to sev- 



