March, 1902.] 4,9 



by the fact that along the East African littoral Gotzius is the dominant 

 species almost to the exclusion of ilitkyia, which prefers the cooler 

 uplands and plateaux of the interior. 



In comparing the wet season forms of these two species the most 

 striking difference which presents itself is the absence in ackeloia of 

 the broad white bauds on the under-side of the hind-wings. There is, 

 I believe, an important significance in this deviation from the colouring 

 of the typical species ; for achcloia, when at rest, presents thereby a 

 notable remsemblance to the wide-spread and distasteful Acrcea 

 Terpsichore L. (A. serena, auctt.), and its various subspecies. This 

 fact will probably throw some light ou the peculiar distribution of the 

 two species of Byblia. For certainly, so far as South Africa is 

 concerned, the ranges of ackeloia and A. Terpsickore-Rougeti, Boisd. 

 {A. Buxtoni, Butl.), are practically coincident ; whereas in the strong- 

 holds of ilitkyia this Acrcea is of rare occurrence, or, more frequently, 

 entirely absent. In the warmer and more luxuriant lowlands the 

 development of bird and butterfly life is at its maximum, and the 

 struggle for existence is consequently keenest. And it is precisely in 

 such localities that ackeloia has ousted ilithyia, which we cau readily 

 understand as soon as we realise the higher protective value of its 

 incipient mimetic colouring. The persistence of the broad white 

 stripes on the under-side (in conjunction with the uniform dark 

 background) in the dry season forms of both species is doubtless due 

 to their procryptic value upon the same principle as the tiger's stripes. 



The following is a detailed description of the larva of B. Gotzius- 

 ackeloia : 



Full-grown larva : — Length, exclusive of cephalic horns, 25 to 30 nun. ; head 

 black, except a broad band of dull green extending from the back of horns to the 

 anterior margin of 2nd segment. The lateral portions of lobes are fairly closely set 

 with short stout white spines of varying lengths, and there are also a few on the 

 vertex ; these spines arc sparsely scattered with very short white hairs. The vertex 

 of each lobe is gradually produced into a very long cephalic horn, measuring about 

 4.5 mm. This horn is only very slightly narrowed to apex, where it is distinctly 

 clubbed, the club bearing a vertical spine surrounded by a whorl of five short thick 

 spines, with usually either one or two additional thinner ones. The main stem of 

 the horn bears nine or ten irregularly placed short spines, much thinner than those on 

 the club, and is also studded with minute setigerous tubercles. The colour of the 

 horn is dark-greenish black and the stem spines black, usually with white bases. 

 TJie horns are placed much more vertically than in Precis, and are thus more nearly 

 in a line with the front of the face ; when at rest the head is bent in sharply so 

 that they project straight out in front. Body cylindrical, set with series of stout 

 branched spines. The spines have a short thick base (1 mm. in the largest), on the 



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