1880.] 



toitli Eemarlcs on the Species allied thereto. 



149 



unquestionably belong, taken as a whole, presents us with a remarkable series 

 o£ gradations in the amount of difference between the sexes, comprising as 

 it does : one species (P. Dravidarum) in which the sexes closely resemble one 

 another in the form of the wings and in colour and markings, and there is only 

 an incipient sexual differentiation : another (P. Mahadeva) in which, while 

 agreeing in structure, they differ to a considerable extent in markings and 

 colour, and the secondary sexual characters of the male are much more 

 pronounced : another (P. Castor) in which they differ from one another 

 to such a remarkable extent that no lesser an authority than Prof. 

 Westwood originally described them under different names and still main- 

 tains their distinctness, and Mr. Wallace* placed them in different groups 

 of the genus ; the male having acquired the most pronounced secondary 

 sexual characters (including rudimentary tails), which have been partially 

 transmitted to some females but not to others ; and the two forms of 

 female having retained, one of them the form of wings, and both the 

 general style of colouring, characteristic of both sexes in the first- 

 named species : and, finally, others (P. Helenus, P. Ghaon, etc.) in which 

 the male has perfectly transmitted to the opposite sex all the secondary 

 sexual characters (including the long tails) that he had acquired, the female 

 only differing from him in such trifling points as the lighter coloration of the 

 outer half of both wings and the dingier shade of her upper surface generally. 



From these and other facts, we are, I think, entitled to infer the pro- 

 bable descent of all the members of this group fi-om an ancestor with 

 tailless, rounded wings in both sexes, closely resembling P. Dravidarum,\>\xi 

 with diffused discal markings in the hind-wings and probably also in the 

 fore-wings ; the conspicuous wing-blotches of P. Helenus, P. Castor, etc., 

 having apparently resulted from the concentration, so to speak, of such 

 diffused colouring in the direction of the breadth of the wing, just as have 

 the discal bands of short spots in P. Dravidarum and P. Mahadeva from 

 a similar pi'ocess of modification in the opposite direction. 



If his conclusions are correctly reported. Prof. Westwood's draw- 

 ings must represent a species different fromeitlier of those alluded to herein, 

 and I look forward with much interest to the appearance of his paper. 

 Explanation of the Plates. 

 Plate VIII. 

 Fig. 1. Papilio JDravidarum, W.-M., ^ . 



Fig. 2. Tapilio Castor, Westw. 5 2nd Form (P. PoUttx, Westw.), from Silhet. 



Plate IX. 



Fig. 1. Fajjilio Castor, Weatw. from Silliot. 



Fig. 2. ? 1st Form, from Silhet. 



r/.-' = third branch of the median vein. 



* In his wuU-kuowu memoir ' On the Phenomena of Variation and Geographical 

 Distribution as illustrated by the PapUioiiidce of the Malayan Region' in Trans. Linn 

 Soc. Lond., vol. xxv, pp. 33, 34. 



