THE SEX OF A PARTHENOGENETIC TADPOLE AND 



FROG 



JACQUES LOEB AND F. W. BANCROFT 



The Rockefeller Institute for Medical Research, New York 



THREE FIGURES 



Bataillon has shown that the unfertihzed egg of the frog can 

 be caused to develop by puncturing it. Last spring we tried the 

 experiment in a large number of eggs of various species of anura. 



The females were separated from the males, carefully washed 

 with water and with alcohol, and then opened. The eggs were 

 taken out of the uterus with sterilized instruments without com- 

 ing in contact with the surface of the frog. About 20 per cent of 

 the unfertilized eggs were kept "as controls and 80 per cent were 

 punctured. A few eggs were fertilized with sperm. Not a 

 single unfertilized control egg segmented or developed. The 

 number of unfertilized eggs which began to segment after punc- 

 ture was greater in the wood frog than in the leopard frog, and 

 amounted in the most favorable cases to about 40 per cent in the 

 former. Only 2 of about 10,000 punctured eggs of the wood 

 ■frog reached the tadpole stage, but these died before they were 

 able to swim. The percentage of eggs of the leopard frog which 

 reached the tadpole stage was greater. From 700 punctured 

 eggs of the southern leopard frog, 13 good morulae were isolated 

 the next day. On the third day, when the fertilized controls 

 were in the gastrula stage, 13 vmfertilized punctured eggs were 

 also in the gastrula stage and 4 more eggs were developing abnor- 

 mally. On the fourth day, 8 of the parthenogenetic eggs had good 

 medullary folds and 4 had irregular folds. On the sixth day, 

 most of the fertilized eggs hatched and 8 of the parthenogenetic 

 eggs hatched also. Of these latter, 4 were developing regularly 

 and 4 irregularly. Those that had not hatched were abnormal. 



275 



