503 



of a specimen of another form, if [specifically the same as the first, then will most 

 probabl}' come within the limits of variation of the first ; if it stands outside those 

 limits one has to examine some more specimens. It is perhaps not unnecessary to 

 repeat that the tailed and taillessyb/«afe of P. menmon have been proted by rearing 

 to belong to one species. 



The second point which strikes one when comparin«; the sexual armature of 

 species of the same group or closely allied groups, and which is of no less great 

 practical consequence, concerns the fact that the species which we mnst regard as 

 more or less close relatives on the ground of their general organisation bear in 

 the structure of the organs of copulation (inclusive of the modified eighth segment 

 of {)!& female) a greater resemblance to one another than to the sjaecies which stand 

 further away in the system. Representative species, such as P. aristeus and rhnsus; 

 aegeus, tydeus, gambrisius, iriopinatus ; euckenor and depilis, etc., have the organs in 

 question built up after exactly the same plan, and the differences exhibited by these 

 representative species in the organs of copulation are often not only far less obvious 

 than the external diflerences of the species, but are sometimes so slight that the 

 degree of divergence between two species is less than the degree of diver- 

 gency between the extreme individuals of one of the two species; we refer for 

 illustration to the figures given of the harpes of P. aef/eus and inopiiiiif(i.<, poh/tes 

 and amhrax. lu less closely related species the similarity in the sexual armature 

 is not so great as in those representative species which are phylogenetically younger 

 forms ; the organs are more divergently developed, and the peculiar modification of 

 one or the other part of the apparatus often obscures the actual homology, so that 

 the organs superficially compared are very dissimilar in appearance. Nevertheless 

 a comparative study at once shows that the superficially dissimilar apparatus are 

 developments of the same type. In P. tiii.rpedon and cloanthus the close relationship 

 of the valves and harpes (f. 96 and 140) is obvious. In aristeun (with rhesus, 

 f. 72 to 82) the oi'gaus are more strongly modified, but the homology of the single 

 parts with those of P. cloanthus is not difiicult to perceive ; antiphates has the organs 

 again similar to those of aristeus, and the externally very dissimilar P. delesserti, 

 leucothoe, and xenocles resemble aristeus in the structure of the male organs to a 

 surprising extent, the principal prehensile parts of the valve consisting in these 

 species, as in aristeus and antiphates, of a ventral dentate ridge, a subdorsal pro- 

 cess, and the dorsal lobe of the bipartite valve, which parts respectively are 

 homologous to e, c, h of f. 72 (aristeus). The vaginal armature agrees in this 

 resjiect with the male armature ; here again the most closely allied species have a 

 greater similarity in the organs in question to one another than to less nearly related 

 species: P. ambrax ami poli/tes (f. 161 and 160); /■". aegeas, rumanzocius, and 

 memnon (f. 166, 170, and 171) ; P. sarpedon, aristeus, agamemnon, and mac/arlanei 

 (f. 182 to 187) illustrate this fact sufficiently. Although it would seem to follow 

 from these statements that the degree of blood-relalionsliip of two species to a third 

 could easily be made out from the degree of similarity in the form of their organs of 

 copulation, this inference of the facts would nevertheless be hasty and most probably 

 erroneous, if we generalised the conclusion so as to apply to every species. Our 

 researches convince us that it is true that in every grouj) of closely allied species of 

 Papilio the characters of the three independently variable organs, wing, harpe of 

 male, and the vaginal armature oi female, are such that each of these organs 

 of every species is morphologically closer related to the respective oi'gan of every 

 other species of tiie group than to that of any species standing outside the group. 



