THE FOEIIATION OF THE LAYEES IN AMPHIOXUS. 325 
Text-fig. 8. 
Median sagittal sections through poi’tions of the eggs of Sturgeon 
(after Deane) ,Hypogeophis (after Brauer) . Tropidonotus (after 
Bellowitz). in order to show the process of gastrulation. s. The 
segmentation cavity, s'. Inner portion of archenteron. a. Outer 
portion of archenteron. 
