Mr. G. A. K. Marshall on the Genus Byblia. 339 



is a small species of nettle which grows on the open veldt. 

 The spiny green ova are deposited on the smaller leaflets, 

 with which they assimilate wonderfully well. The larval 

 stage is interesting in that it exhibits a very curious instance 

 of dimorphic coloration. The two forms are as follows : — 



(1) Green form. 



Length about 1 inch. Dull green, with a double 

 light yellowish central line. Each segment has on 

 its anterior edge three black spots, one in the middle 

 of central line and the others on each side of it. A 

 very indistinct narrow lateral line of pale green. A 

 small brownish dot on each segment below lateral 

 line, those on thoracic segment being larger. Each 

 segment has a transverse row of six dorsal tubercles, 

 from each of which springs a stout spine ; about 

 halfway up this is a whorl of five smaller spines ; 

 stem of main spine green, apices of small spines 

 broadly blackish. A similar smaller branched spine 

 just above the legs entirely pale green. Whole of 

 upper surface closely covered with minute white seti- 

 gerous tubercles. Head green, with eyes and a broad 

 frontal stripe brownish black ; green portion studded 

 with short whitish bristles, the longer ones being black- 

 tipped. On vertex two long blackish branched spikes, 

 longer than those on abdomen and markedly clubbed 

 at apex. 



(2) Black form. 



Ground-colour dull black, with a broad pale yellow 

 median stripe, divided centrally by a narrow black 

 line ; a broad, irregular, reddish-brown lateral stripe, 

 ill-defined along its superior edge ; this stripe has on 

 each abdominal segment three downardly oblique 

 black lines, of which the upper one is longest and 

 passes through spiracle, and the middle one is very 

 short. Ventral area, legs, and prolegs black, the 

 latter pale at apex. Head black, with short whitish 

 bristles. 



The meaning of this dimorphism is at present by no means 

 clear to me. The green form is well protected by its assimi- 

 lation to the hairy green leaf of the nettle, but tlie black one 

 is a very conspicuous object on the food-plant. At first I 

 suspected that it might be a matter of sex, the female being 

 the protected form. But, unfortunately for ray theory, 



