This paper describes a method for transplanting living nuclei from blastula cells into enucleated frog eggs. The authors, Robert Briggs and Thomas J. King, detail the technique and its successful application in experiments. They begin by discussing the role of the nucleus in embryonic differentiation, noting that while early cleavage nuclei are considered identical, their potential for differentiation remains untested. The method involves pricking the recipient egg to activate it, removing the egg nucleus, and injecting a blastula cell nucleus into the enucleated egg. The results show that when the donor nucleus is from the same species as the egg cytoplasm, the egg cleaves and develops normally. When the donor nucleus is from a different species (R. catesbeiana), the enucleated egg forms a blastula that arrests and dies, similar to the hybrid between the two species. This experiment confirms that blastula cell nuclei can be transplanted without significant damage, making the technique useful for studying nuclear differentiation and other nuclear functions. The authors also discuss the potential for refining the method to eliminate cytoplasm and further explore the role of the cytoplasm in nuclear function.This paper describes a method for transplanting living nuclei from blastula cells into enucleated frog eggs. The authors, Robert Briggs and Thomas J. King, detail the technique and its successful application in experiments. They begin by discussing the role of the nucleus in embryonic differentiation, noting that while early cleavage nuclei are considered identical, their potential for differentiation remains untested. The method involves pricking the recipient egg to activate it, removing the egg nucleus, and injecting a blastula cell nucleus into the enucleated egg. The results show that when the donor nucleus is from the same species as the egg cytoplasm, the egg cleaves and develops normally. When the donor nucleus is from a different species (R. catesbeiana), the enucleated egg forms a blastula that arrests and dies, similar to the hybrid between the two species. This experiment confirms that blastula cell nuclei can be transplanted without significant damage, making the technique useful for studying nuclear differentiation and other nuclear functions. The authors also discuss the potential for refining the method to eliminate cytoplasm and further explore the role of the cytoplasm in nuclear function.