^^ 



PAPILIO III., IV., V. 



So that the black form appears constantly in the spring as well as the summer 

 brood. The difl'erence between the summer and winter form of the black female 

 in size and ornamentation is well shown in Plates III., IV., the first of these 

 being the summer. 



From eggs obtained in same way from yellow females, there resulted in the 

 s^pring of 1872, 8 -^, 3 ^ all yellow. In August, 1875, 3 <^, 12 « all yellow, and 

 from part of the chrysalids of this lot which passed the winter, there appeared in 

 the spring of 1876, 4 '^ , 12 yellow *, 1 black *. This is the only instance out of 

 many broods raised, in which a black has come from a yellow mother, though on 

 two occasions, besides the one above mentioned, a yellow female has come from 

 black. 



Mr. Darwin lays much stress upon the prepotence of transmission, in the case 

 of pecuHarities transmitted through one sex only of a species, and asserts that 

 " characters may first appear in either sex and afterwards be transmitted to the 

 offspring of the same sex." " Variation of Animals," etc., 1st Am. ed., II., p. 106. 



That yellow females should rarely produce black is not surprising, but that 

 the reverse should not often and constantly happen, inasmuch as the blacks are 

 always crossing with the yellow males, does indicate an amazing energy in the 

 black form, and implies a time when the yellow female will wholly succumb to 

 the other throughout the regions now inhabited by the two, unless there be in 

 certain districts some restraining influence, as climatal, or the existence of ene- 

 mies. To the northward, and in elevated districts, there must probably be same 

 restraining climatal influence on the black form. No black Papilio of any species 

 is found in the sub-boreal regions, though on both continents, and at great ele- 

 vation, the yellow Machaon flourishes, as does Tiirnus in North America. 



Mr. Wallace, " Natural Selection," p. 154, speaking of Turnus and its dimor- 

 phism, considers it " highly probable that the existence of enemies and of com- 

 peting forms of life, may be the influences whicli determine the relative propor- 

 tions of each form ; " and hopes that observations may ascertain " what are the 

 adverse causes which are most efficient in keeping down the numbers of each 

 of these contrasted forms." 



In looking for the causes of the decrease of the yellow female in the western 

 and southwestern districts, and the manifest luxuriance of the black, it seems to 

 me that it is not unlikely largely owing to the facility with which the yellow 

 females are captured by birds and other enemies by day. They are slower of 

 flight than the males, and when heavy with eggs, are very sluggish, flying but 

 little and at short distances, and their gay color renders them an easy prey. It 

 IS true, the black females ai-e equally slow of flight, but they are less easily seen, 

 and as other species of black Papilios, Troihis, Philenor, and Asterias, are always 



