312 Dr. T. A. Chapman on a new form of seasonal 



first-brood (spring emergence) and the single-brooded form 

 of A. tlier sites to be most nearly related to A. escheri, i. e. 

 having with it a not very remote common ancestor, it 

 follows that the second (summer) brood is of more modern 

 evolution. Whether in this brood the androconia are fol- 

 lowing the general facies in approaching P. icarus, involves 

 discussion for which data are too scanty. 



The identity in the genitalia and again in these andro- 

 conia of the first brood and especially of the single brood of 

 A. ther sites with those of A. escheri suggests strongly, if it 

 does not prove, that A. thersites and A. escheri have a common 

 origin and are nearly related, and, on the other hand, that 

 the close resemblance between A. thersites and P. icarus 

 is superficial and of the nature of convergence, due perhaps 

 as much to actual mimicry as to other circumstances such 

 as habits and habitat. 



I have examined a few specimens of P. icarus and of 

 A. coridon and A. thetis, in search of a similar seasonal 

 dimorphism in the androconia. It is certain that if there 

 be any such dimorphism, it is not abundantly obvious as in 

 the case of A. thersites, and would require a much larger 

 number of observations than I have made to establish ; at 

 the same time there is a certain amount of variation that 

 may be individual, but sufficient to prevent my asserting 

 that no such dimorphism exists, though I am almost inclined 

 to assert that there is no trace of it in P. icarus. 



To sum up, A. thersites has so close a resemblance to 

 P. icarus that for 50 or 60 years no one has chosen to question 

 their identity, yet A. thersites has genitalia in both sexes 

 identical with those of A. escheri except in size, and very 

 different from those of P. icarus; it has also androconia 

 practically identical with those of A. escheri, this is true only 

 of first-brood (when digeneutic) and single-brood specimens. 

 Second-brood specimens have a very different form of 

 androconium, more like (but still abundantly different from) 

 that of P. icarus. 



So far as I know this is the first record of seasonal (or 

 other) dimorphism in these battledore scales. 



That this more primitive and more typical scale of thersites 

 was unknown to me till my attention was called to it by 

 Mr. Ball, is due to the circumstance that the monogeneutic 

 race of A . thersites was unknown till I discovered it last summer 

 at Le Lautaret, and that the first-brood specimens are 

 probably much less numerous than those of the summer, 



