APPEARANCE OF THE SOMITES IN THE CHICK. 



125 



neural tube is slightly injured. Aside from this the embryo is 

 normal in every way. The eighth pair of somites is just being 

 cut off and the heart is forming. 



A sagittal section through the somites of this embryo confirms 



^< ' •)> • '■■ ■ 



■ ■■ 











Fig. I. Twenty-one hours old. It shows the first pair of clefts, which meet the 

 main axis of the embryo at an oblique angle. The place of injury is shown at 0. 



X20. 



Fig. 2. Twenty-two hours old when operated on, and then incubated ten hours. 

 It shows eight pairs of somites, and the injury in the right anterior somite at O. 

 X20. 



what is seen in surface view. The rudimentary somite is greatly 

 injured (Fig. 3, x) and its characteristic enlargement (see Figs. 

 10-12) is not present. 



