1028 



A. W. BLACKLER AND M. FISCHBERG 



The egg of Xlp is smaller than that of Xll (1.10 mm. as against 1.35-1.50 mm). 

 The animal hémisphère of the egg of XI 1 is covered with a chocolate-brown 

 pigment and the végétal hémisphère is white, but three zones may be distinguished 

 in the egg of Xlp, — a dark brown animal zone, a cream-coloured marginal zone 

 and a pale brown végétal zone. When the third cleavage takes place in Xlp the 

 animal pigment is neatly separated from the creamy marginal zone by the furrow, 

 but in XI 1 some of the animal pigment remains below the furrow. 



In later development Xlp resembles X. 1. victorianus (see Blackler, Fisch- 

 berg and Newth 1965 for détails) more closely than XI 1, especially in the timing 

 of melanophore production. The first true melanophores appear slightly later in 

 Xlp than in XI 1 (stage 36 as against stage 33 of the Normal Table) and melano- 

 phores are not found in the tadpole tail until stage 40 (stage 37 in XI 1). Melano- 

 phores are manifest in the région of the rectal tube at stage 50 in Xlp but do not 

 appear until shortly before the onset of metamorphosis in Xll (stage 57). 



The process of metamorphosis requires the passage of 12 days in Xlp and 9 

 days in Xll at 22° C. The resorbing tail remains laterally flattened in Xll and has 

 a strong curl toward the dorsal side, but becomes cylindrical with only a very 

 slight dorsal bend in Xlp. 



I 



Development and Characters of the Reciprocal Hybrids 



a) A7/Ç x Xlp$\ We have performed this cross three times and each time we 

 have been able to obtain good development. Although some abnormalities are 

 found in the embryonic period, thèse are variable and most likely fall within 

 the usual limits of abnormal development for hormone-provoked spawnings. 

 Over 75 % of ail blastulae developed into metamorphosed toads. 



The fertile eggs were, of course, normal Xll eggs and they developed in a 

 typically laevis manner up to the feeding tadpole stage. The true melanophores 

 made their appearance at stage 33/34. The présence of the Xlp génome first made 

 itself manifest at stage 50 when melanophores appeared over the région of the 

 rectal tube. 



During metamorphosis the resorbing tail was cylindrical in section, thereby 

 recalling a petersi character, but the tail curled dorsally rather more than is usual 

 for Xlp but always somewhat less than in pure laevis. 



After metamorphosis the ventral surface of the hybrid was initially white but 

 during the first year yellow pigment was gradually deposited, especially on the 

 undersides of the legs, and black spots began to form and spread from the legs 

 toward the head (figs. 6 and 7). Référence has been made above to the variability 

 of the dorsal patterns and it is worthy of note as far as the hybrid is concerned 

 that its dorsal colouring and pattern always resembled the Xlp type and never 

 the Xll pattern (fig. 8). 



