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HYBRIDIZATION AND EARLY DEVELOPMENT 



RECORD OF THE EXPERIMENTAL DATA FROM HYBRID CROSSES 



Hamburger, 1936, has hybridized three European species of Triton, namely cristatus, 

 taeniatus (formerly vulgaris) and palmatus (formerly helveticus). The crosses were nnade 

 both ways but some were more viable than others. Recently (1947) Connon hybridized 

 three species of California Tritons, namely torosus, rivularis, and granulosa (formerly 

 similans, Twitty, 1942). If the oviduct of the ovulating Urodele is opened and the eggs 

 are transferred into a concentrated sperm suspension in Standard Solution, hybridization 

 can be achieved. In these forms where development can be carried quite far, the inher- 

 itance of pigment patterns may be studied as they are influenced by maternal and paternal 

 genes. 



By combining hybridization with androgenesis Porter (1941) has ingeniously discovered 

 that there are two (morphological) varieties of Rana pipiens. One he collected in Ver- 

 mont and the other near Philadelphia. These differences are not normally found, even 

 though the crosses may be frequently made, because in normal hybrids the nuclear dif- 

 ferences are compensated for by the cytoplasmic differences and the resulting larvae are 

 normally viable. ** 



* Condition refers to any variahles concerning either of the gametes such as prior irradiation with x-rays, or ageing of the eggs, etc. 

 ** If x-ray facilities arc available, it is instructive to irradiate the spermatozoa of any of the crosses in Group 2 on the following 

 page with at least 10, 000 r units prior to the insemination of the eggs of the other species. Generally some of these eggs will 

 pass the critical stage of gastrulation. (See Rugh and Exner, 1940. ) 



