E. HOFF-J0RGENSEN 



(2) DNA in embryos during the early stages of development : 



150 



100 



-'/2 3/y 1*/z 3 1'/2 6 m 



hours after fertilization 



Figure 2. Table: Percentage of embryos (Paracentrotus lividus) at differ- 

 ent stages of development. Graph : Content of DMA per embryo or egg. 



Figure 2 shows that the content of DNA in the embryo is the same as in the unferti- 

 lized eggs until the 16-cell stage. 



DNA IN EGGS, SPERM AND EMBRYOS OF RANA TEMPORARIA 



Material. The eggs were fertilized as described by Rugh (1948). The jelly was re- 

 moved with scissors. The eggs and embryos were dried with acetone and ether. In 

 sperm DNA was determined without drying. 



Results 



(1) DNA in sperm and unfertilized eggs: 



(a) sperm 



4 ml. sperm suspension ~ 1 4 x io 6 sperm ^ 12 -6 /ng. DNA 

 per sperm: 8-6 x io -6 /ng. DNA 



(b) unfertilized eggs 



25 eggs ~ 1 -73 /xg. DNA 



25 » ~ I/9 1 » » 

 25 » ~ 1-82 „ „ 



84 



