Fig. 6. Section tlirough the head of an embryo at a stage intermediate 

 between F and G. x 86 diameters. 



It shews the manner in wliich the medullary folds of the head unite to 

 form the medullary canal. 



Fig. 7. Longitudinal and vertical section through the tail of an embryo 

 belonging to stage G. 



It shews the direct communication which exists between the neural 

 and alimentary canals. 



The section is not quite parallel to the long axis of the embryo, so that 

 the protovertsbrre are cut through in its anterior part, and the neural canal 

 passes out of the section anteriorly. 



Fig. 8. Network of nuclei from the yolk of an embryo belonging to 

 stage H. 



