HEAD-FOLD TO TWELVE SOMITES 113 
but this arises normally at the stage of 12-14 somites, a very 
short distance in front of the first somite of the series, which is 
thus shown to have the same position as the first somite formed. 
On the other hand, if one assumed that the first somite formed 
TLE 
L 
2.0. ps 
Fic. 66. — The same embryo from beneath, drawn in alcohol with 
reflected light. Abbreviations as before. 
became the third or fourth of the series, it is clear that one would 
have to make a mark some distance in front of the first somite 
formed, to strike the place of origin of the otocyst. Marks made 
on this theory were always found a considerable distance in 
front of the otocyst. Altogether a large number of experiments 
