124 



HYBRIDIZATION AND EARLY DEVELOPMENT 



CuBAL nOTOCmObO 



Embryo formation in normal development and in the pipiens ° X sylvatica o hybrids. O, M, 

 S, and H represent the cells of the invaginating material that will ultimately be found adjacent 

 to the olfactory organ, mouth, sucker, and heart. OLF, olfactory organ; OPT, optic vesicle. 



Moore (1946) has found that in hybrids between Rana pipiens females and Rana sylvatica males 

 that development is normal to early gastrulation. The arrested gastrulae remain alive for a 

 number of days, and show restricted invagination of the dorsal lip region. This is illustrated in 

 the accompanying diagrams. 



(From Moore 1946; Jour. Exp. Zool. 101:173) 





Fig. 1. A typical Rana pipiens female. Fig. 2. A typicoj Rana bums! female. Figs. 3 to 6: Hybrids from various 

 crosses. Fig. 3. pipiens female x pipiens male. Fig. 4. bums) female x bumsi male. Fig. S. pipiens female x 

 bumsi male. Fig. 6. bumsi female x pipiens male. 



In Figs. 5 ond 6 note that the bumsi young hove spots on the hind legs. This is probably indication of their heterozy- 

 gous (Bb) nature. In Fig. 4 some of the bumsi have spots on the hind legs (upper row) while the two at the lower left 

 ore devoid of the black leg spots. The former are probably Bb and the non-spotted. 



Figs. 7 and 8 - two types of tadpoles, spotted and non-spotted. The spotted tadpoles in most cases give rise to pipiens 

 young, and the non-spotted tadpoles, in most cases, give rise to bumsi young. 



(Courtesy J. A. Moore 1924: Genetics 27:408) 



