112 THE DEVELOPMENT OF THE CHICK 
first place the position of the first somite was marked with a 
delicate electrolytic needle which left a permanent sear. The 
eges thus operated on were closed up and permitted to develop 
to a stage of 10-12 somites or more; and then the mark was found 
Fig. 65. — Embryo of 12s, from above, drawn in alcohol with re- 
flected light. 
au. ep., Auditory epithelium. Other abbreviations as before. 
to coincide with the first somite of the series. In the next place 
it was possible by similar means to mark out the topography of 
the embryonic head in the stage of one or two somites. Thus 
it was determined that a mark made immediately in front of the 
first somite formed appeared later in the region of the otocyst; 
