Certain Forms of the Genus Acraea. 295 



though it may well be as he states. Greater differences 

 than this occur in the genital plates of forms of A. acrita, 

 but do not enable us to define specific limits to those forms. 

 The alleged difference in the uncus in the two species 

 does not appear to me to be valid. The organ in both 

 species is curved in a vertical plane. If Professor Houlbert 

 alludes, as I think he does, to a curve in the horizontal 

 plane, such an appearance in a dry specimen is of no value 

 whatever, since the organ is frequently distorted through 

 desiccation. In the many dissections I have made, I have 

 never found the uncus in any Acraea to be curved 

 laterally when once its flexibility has been restored by the 

 caustic treatment. Such a curved condition would be a 

 form of asymmetry, a phenomenon which, so far as my ex- 

 perience goes, does not occur in any species in the male, 

 though one or two females have an asymmetrically placed 

 copulatory orifice (neobule, etc.). In my opinion, the male 

 armatures of masamba and siliana are not distinguishable 

 when the features of these organs are considered as a whole 

 and in relation to those of other species of the genus. In 

 some genera the male armatures are practically indistin- 

 guishable, and so useless for specific distinction, but the 

 genus Acraea is remarkable for the constant infra-specific 

 differences in the genitalia. 



Now as to the scales. On Plate LXXIV I have illus- 

 trated sixteen examples of scales in an endeavour to confirm 

 Professor Houlbert's conclusions. Figs. 1-5 are taken from 

 the fore-wing apical area of A. masamba, and figs. 6-10 

 from the same area in A. siliana. No two are exactly 

 alike, nor do any quite resemble Professor Houlbert's 

 figures on p. 169 of the paper referred to. In spite of 

 diligent search I could find no scales which had not the 

 deeply indented " shoulder " at the base, shown in my ■ 

 drawings, but quite absent in those of Professor Houlbert. 

 Figs. 11-13 are from the fore-wing internal angle of masamba, 

 and figs. 14-16 from the same area in siliana. So far as I 

 can judge, the outlines of the scales are so variable that 

 they do not furnish a character which is useful in this case 

 for specific distinction. Nor is the outline of scales an 

 entirely satisfactory character for the purpose, since my 

 friend Dr. F. A. Dixey has found that even the Pierine scent 

 scales, so characteristic in most cases, show considerable 

 variation in different individuals of G. napi. 



Let us then sum up the whole matter : The most essential 



