PLATE 4 



EXPLANATION OF FIGURES 



15 10-mm. Chelydra (same series as fig. 14). Sagittal section cutting lower 

 edge of ganglion ciliare and the outer disintegrating wall of the first head somite. 

 X 135. 



16 Same series. Section passing through the ej^e and the mandibular divi- 

 sion of the trigeminal nerve. X70. 



17, 18 10-mm. and 11-mm. embryos respectively, showing the relations of the 

 Mm. rectus lateralis and retractor oculi. X 135. 



172 



