PLATE I 



EXPLANATION OF FIGtTRES 



1. Spherical egg showing a short anterior and a long posterior depression. 



2. The two germinal depressions very closely united. 



3. The anterior germinal depression after the posterior depression has dis- 

 appeared. 



4. The anterior germinal depression, with the posterior depression at the 

 point of disappearing. 



5. Appearance of the peripheral groove marking out the area of the neural 

 plate. The anterior and posterior germinal depressions are distinguishable 

 and there is the beginning of the transverse cephalic groove on the left side. 



6. The transverse cephalic g^roove fully formed on the right side. The posterior 

 germinal depression is absent. 



7. A very deep transverse cephalic groove particularly on the left side. The 

 newly formed neural groove is seen, being especially well marked in the posterior 

 half of the neural plate. The neural crest is visible on the right side. 



8. The faint appearance of one neuromere. The neural crest is fully formed. 



9. The appearance of one neuromere at the posterior end of the cephalic plate. 

 This photograph shows the relation of the neuromere to the anterior germinal 

 depression. 



10. The appearance of all four neuromeres. The first is the least defined and 

 the second is much the largest. 



11. The four neuromeres seen from the side. The posterior borders of the 

 second, third and fourth neuromeres appear as dark bands. The position of 

 the first neuromere is well defined. The procephalic lobes are raised above the 

 jevel of the rest of the plate. 



12. The infundibular depression and behind it three well marked neuromeres. 

 the second, third, fourth. 



13. Infundibular depression and three neuromeres. 



14. Infundibular depression and three neuromeres. 



15. Infundibular depression and three neuromeres. 



