Certain Forms of the Genus Acraea. ' 291 



qu'une idee tres imparfaite de l'armature genitale des 

 Acraea." I agree entirely that my " two little diagrams " 

 " can only furnish a very imperfect idea of the genital 

 armature in Acraea." They were not made with any such 

 comprehensive purpose in view, but merely to illustrate 

 the most essential differences between the two species 

 igati and damii. My monograph runs to some 375 pages 

 and over 250 illustrations. To have dealt with the detailed 

 structure of the armatures of the 140 species of Acraea 

 would have required another volume of similar dimen- 

 sions, and would scarcely have served an advantageous 

 purpose. 



The second part of Professor Houlbert's interesting con- 

 tribution deals with the sphragis, or seal, found on the 

 female of most species of Acraea after pairing. That this 

 structure is of great interest, and its function somewhat 

 obscure, I certainly agree, but I cannot think that Pro- 

 fessor Houlbert has thrown much light on the subject by 

 declaring, as he does, that the sphragis is not the result 

 of a secretion deposited by the male on the abdomen of 

 the female. It is true that the process of formation has 

 not, so far as I am aware, been actually observed in the 

 case of an Acraea. A homologous formation occurs, how- 

 ever, in at least seven other genera of butterflies, and in 

 the case of Parnassiiis the process of formation has been 

 investigated by Mr. Arthur Thomson, and the subject is 

 dealt with at some .length by Mr. H. J. Elwes in his paper 

 on Parnassius in Proc. Zool. Soc. Lond., p. 6 et sea., 1886. 

 In my monograph I referred to this article, but did not give 

 extracts from it, thinking that the investigations mentioned 

 were sufficiently well known. I would refer Professor 

 Houlbert, and others who may be interested, to this paper. 

 He will there see that the " pouch " is produced during 

 copulation, and that there is exuded from the abdomen of 

 the male a gelatinous substance which hardens rapidly on 

 exposure to the air, and retains in its hardened condition 

 impressions made upon it whilst in the viscous state. The 

 sphragis in Acraea being a formation homologous with that 

 in Parnassius, there is every reason to suppose that its 

 origin is of the same nature. On p. 8 of my monograph I 

 pointed out that Marshall had observed no less than three 

 female Acraeas in which the sphragis had been duplicated, 

 though both formations were more or less distorted in 

 shape, " indicating that the second pairing must have 



