2 Normentafeln zur Entwicklungsgeschichte der Wirbeltiere. 



Fig. 8. (X lo.) 

 Side view of egg 2 days I2 hrs. old. The upper surface of egg shows some five hundred cells, the 



lower about forty. 



Fig. 9. (X lo.) 



Top view of egg 4 days 4 hrs. old. Segmentation cavity shows through thin translucent roof. 

 Blastopore not präsent. 



Fig. 10. (X 10.) 



Bottom view of egg 6 days 16 hrs. old. Crescentic blastopore. Line of invagination sharply 

 separates large yolk cells from small cells of blastodisc. 



Fig. II. (X 10.) 

 Dorso-lateral view of egg 10 days 10 hrs. old. Large circular blastopore; faint indication of 

 embryonic anläge. 



Fig. 12. (X 10.) 



Side view of egg 10 days 16 hrs. old. Large circular blastopore. Anlage of mesial portion of 

 embryo above dorsal lip of blastopore. Segmentation cavity faintly outlined. 



Fig. 13- (X 10.) 

 Top view of egg 13 days 3 hrs. old. Small circular blastopore. Embryonic anläge triangulär in 

 outline ; lateral boundaries indistinct. First appearance of neural groove. Roof of segmentation cavity 

 thinner, making its boundaries distinct. 



Fig. 14. (X 10.) 



Top view of egg 14 days 4 hrs. old. Blastopore smaller, lateral margins of anterior portion of 

 embryo bounded by short broad ridges which are the beginnings of the lateral portions of the neural 

 fold. At anterior margin of embryo there is a transverse crescentic ridge which is beginning of transverse 

 portion of neural fold. Neural groove deep but does not extend either to transverse portion of neural 

 fold or to blastopore. Segmentation cavity crescentic. 



Fig. 15- (X 10.) 

 Top view of egg 14 days 19 hrs. old. Blastopore much reduced, circular. The yolk plug is not 

 visible in this egg. Lateral and transverse portions of neural fold united to form continuous fold around 

 anterior portion of embryo. Lateral boundaries of posterior portion of embryo not defined. Neural groove 

 not as long, nor as distinct as in preceding stage. Dark crescentic area in front of embryo is segmen- 

 tation cavity. 



Fig. 16. (X 10.) 



Top view of egg 15 days 15 hrs. old. Blastopore small, circular; yolk plug visible. Neural fold 

 prominent, its free ends extend nearly to blastopore. Neural groove deep and narrow at anterior end, broad 

 and shallow at posterior end, fades out just in front of blastopore. A part of the segmentation cavity is 

 still apparent in front of the embryo. 



Fig. 17. (X 10.) 

 Top view of egg 16 da3's 6 hrs. old. Blastopore reduced to a very minute circular aperture. Neural 

 plate narrower than in preceding stage. Neural fold prominent, its free ends coalescing at blastopore. 



