1024 



A. W. BLACKLER AND M. FISCHBERG 



with Parker's conclusion. Finally, borealis (like X. 1. laevis) may measure over 

 100 mm. in length. However, borealis and laevis are geographically isolated, since ! 

 borealis is a résident of Kenya. 



For embryological purposes, the précise systematic status of thèse subspecies j 

 is in gênerai not important, although it has been our expérience that there are i 

 sufficient différences in their developments to render certain types of expérimental 

 work rather confusing. However, given that most European and American labo- 

 ratories have obtained their animais through South African dealers, it is reasonable 1 

 to assume that published articles refer to X. 1. laevis unless the contrary is spe- 

 cified. If there is sometimes confusion, it is more likely to resuit from the facti 

 that the species X. mulleri is often mistaken for X. 1. laevis. This former is a 

 Congo species and thus has entered laboratories via Belgian agencies. 



Be that as it may, we have been concerned in our laboratory with the trans- 

 plantation of nuclei and germ cells between the subspecies and species of Xenopus 

 (Gurdon 1961, 1962; Blackler 1962; Ortolani, Fischberg and Slatkine 

 1966) and thus, for us, distinction between the différent kinds of toads has been 

 an important matter. The interprétation of our results must rest to some extent 

 on the validity of Parker's systematic studies, and in conséquence we have been 

 obliged perforée to attempt hybridizations as a test of taxonomy. Recently wej 

 have given an account of some work which supports the view that X. 1. victoria- 

 nus and X. 1. laevis are indeed true subspecies in a developmental sensé (Blackler, 

 Fischberg and Newth 1965). Below we présent some of our expériences gained 

 in crossing X. 1. peter si with X. 1. laevis. 



Material and Observations 



The X. 1. peter si toads we used (hereafter referred to as Xlp) were sent direct 

 by air from N. Rhodesia. If Schmidt and Inger (1959) are correct in claiming 

 that poweri is a distinct subspecies from petersi then our toads should be referred 

 to as poweri. However, for the purposes of this communication we prefer te 

 folio w the view of Parker 1956. The X.l. laevis toads employed (now referred te 

 as XI 1) were of unknown origin and taken from a laboratory stock: in our expé- 

 rience the différence between such toads and spécimens freshly imported froir 

 South Africa is small, except that the latter are alvvays somewhat larger. 



Characters of the Adult Toads 



Female Xlp may measure up to 80 mm in body length although the majority 

 of individuals are in the 70-74 mm. range. The average weight is 34 gms. Maie; 

 measure about 56 mm. and have an average weight of 19 gms. The toads an > 

 easily bred under laboratory conditions and mature individuals may be obtainec 



