HYBRIDIZATION OF XENOPUS 



1031 



fnophores was slightly delayed (stage 35/36) and they did not appear on the tail 

 luntil stage 40. Another clear Xlp influence, already noted in the reciprocal hybrid, 

 was that the rectal tube melanophores could be observed at stage 50. For the rest, 

 the metamorphic and immédiate post-metamorphic events were the same as for 

 ïthe reciprocal hybrid. 



The colour characteristics of the adults of this combination are also the same 

 as for the other but the proportions of the animais are rather smaller. At 4 l / 2 

 years of âge females averaged 70 mm. in length and 40 gms. in weight, while the 

 maies averaged 50 mm. and 16 gms. respectively. Thèse figures are perhaps more 

 pomparable with petersi than with laevis but they show distinct hybrid character 

 jall the same. 



(Fertility and development of hybrid intercrosses 



Both sets of hybrids showed a normal sex ratio and no animal was found to 

 be stérile. Intersib crosses have been used throughout and ail have given appre- 

 :iable numbers of cleaving eggs. The following remarks apply equally to both 

 hybrids. 



The eggs laid by the females have always measured between 1.1 and 1.2 mm. 

 and showed three bands of egg pigment as in Xlp. The first two cleavages are méri- 

 dional, but the third does not eut off the animal pigment from the rest of the egg. 

 Melanophores make their appearance at stage 33/34 but do not become visible 

 on the tail until stage 40. The melanophores over the rectal tube région appear 

 without exception at stage 50. Thus development up to this stage shows a segre- 

 gated interplay of laevis and petersi influences. Thereafter development up to the 

 înd of metamorphosis is as under the original hybrid crosses. We have not kept 

 :oads after metamorphosis. 



li 



ifl* Discussion and Conclusions 



l 



ice Our expérience in hybridizing thèse toads support the thesis that they are 

 tk .rue subspecies. There does not seem to be any incompatability between the geno- 

 jlj :ypes. As in the case of our study with victorianus, we find that characters of both 

 jlj mbspecies may be found in the hybrids and that often the influence of one subspe- 

 j[ { :ies for any particular character expresses itself at the expense of the other. Inter- 

 1C | nediate characteristics are not very striking. 



^ When Xlp is the maternai parent the hybrids are about the same size (length 

 i0 . ind weight) as Xlp. On the other hand, the reciprocal hybrid tends to be somewhat 

 onger than Xlp but is even more noticeably heavier. Thèse facts could be taken to 

 nean that some maternai influence is at work which is not expressed by the geno- 

 | a . ype of the hybrids per se. 



