32 Mr. G. A. K. Marshall on Seasonal Dimorphism 



one pupating on the 31st March, the other not till the 

 5th April. The former produced sesamus on the 15th April, 

 and the latter emerged on the 20th, producing, curiously 

 enough, pure o.-natalensis. From a third female I secured 

 one egg on the 6th March; this hatched on the 12th; the 

 resulting larva pupated on the 7th April and emerged on the 

 30th as full sesamus. 



The females of this species, like many other Nymphalina*, 

 are somewhat dilatory in their method of ovipositing and 

 often take a long time making up their minds where to deposit 

 an egg ; indeed they seem unable to lay them in anything 

 like quick succession, in which they differ notably from most 

 Pierinas. I have seen Belenois mesentina lay 80 eggs 

 straight off, with scarcely a pause and on a single leaf. The 

 food-plant of sesamus in Salisbury is a low straggling plant, 

 of almost creeping habit, which grows in somewhat matted 

 clumps on the slopes of wooded kopjes. The egg is placed 

 anywhere on the stem or leaves, and in one instance I saw 

 one deposited on a piece of grass adjoining the food-plant. 

 Compared with the size of the insect the egg seems small, 

 the vertical axis is longer than the horizontal, the shape 

 being that of an obtuse cone ; from a circular shallow depres- 

 sion on the vertex radiate 13 (sometimes 12) vertical lamelli- 

 form ridges, which under a pocket-lens appear to be delicately 

 fluted transversely ; the whole egg is glabrous and of a pale 

 glaucous green colour. As will be seen from the dates given 

 above, the oval stage in autumn lasts about six days. The 

 larva on exclusion is dull sepia-brown in colour, being paler 

 towards extremities and set with long black hairs ; the head 

 is black. The hairs develop into spines after the second 

 moult. The description of the full-grown larva is as 

 follows : — Length about 35 mm. ; ground-colour dull velvety 

 black (varying sometimes to very dark crimson) ; a narrow 

 central black line, on each side of which are four short 

 transverse yellow lines on each segment ; these become almost 

 obsolete anally, whereas on third segment they coalesce, 

 forming a large dorsal yellow patch divided in its posterior 

 half by the dark central line ; second segment entirely yellow, 

 with a short transverse central black bar ; a broad macular 

 yellow lateral stripe much dilated on thoracic segments. 

 Each segment bears a transverse row of six long, stout, 

 branched spines, which are black with a distinct dark blue 

 metallic reflection, and two smaller ones placed longitudinally 

 just above legs. Head with a deep central impression on 

 vertex (almost bifid), testaceous yellow with a large lateral 

 spot and a broad frontal V-shaped mark black, mouth 



