MORPHOGENETIC MOVEMENTS 427 



Place carbon (blood charcoal) particles on the Hansen's Node, directly in front 

 of it, and at one or more levels of the Primitive Streak (see figures above). In- 

 dicate by parallel charcoal marks on the medium exactly where these particles 

 are placed. These marks to be used as reference marks later. Watchmaker's 

 forceps may be used for this marking. The forceps may be dipped into the char- 

 coal, shaken of all excess particles, and then touched to the relatively dry upper 

 surface of the blastoderm. There is sufficient moisture to provide a sticky sur- 

 face so that the carbon particles will come off the forceps very readily, and will 

 remain adherent to the blastoderm. 



After 24 to 48 hours examine the blastoderm, cultured in vitro, for any change 

 in the position of the carbon particles. It will, of course, be necessary (as al- 

 ways) to make sketches at the beginning and at the termination of the experiment. 



SKETCH BELOW THE OBSERVED MORPHOGENETIC MOVEMENTS 



