364 JORDAN. 



PLATE XVII. 



Fig. 34. Surface view of living egg, showing depression of yolk-cells (X 20). 



Fig. 35. Surface view of preserved egg, showing semi-lune blastopore. 



Fig. 36. Surface view of preserved egg, showing unusually large circular 

 blastopore, yp., yolk-plug. 



Fig. 37. Surface view of living egg, showing blastopore closing "from behind 

 forwards." 



Fig. 38. Surface view of preserved egg, showing blastopore " closing in both 



directions." 



Fig. 39. Surface view of living egg, in somewhat later stage than Fig. 38. 



Fig. 40. Surface view of preserved egg. The blastopore [prg.) — or primitive 

 groove — is now a narrow slit opening into the mesenteron. 



Fig. 41. Top view of same egg as that shown in Fig. 40. 



Fig. 42. Surface view of preserved egg. First appearance of neural folds. 

 Neural groove terminates in front of the neuropore, np. The blastopore has 

 closed in the middle, leaving open, however, an anterior neuropore and a posterior 

 anus, a. 



Fig. 43. Surface view of preserved egg. The anus lies at the posterior limit 

 of the neural folds. 



Fig. 44. Dorsal view of preserved egg. Neural folds widely separated. 



Fig. 45. Dorsal view of preserved egg, in somewhat later stage than that 

 shown in Fig. 44. The neural folds have approximated, and the neural groove 

 has deepened. 



Figs. 46-48. Vertical median sections through eggs in different stages of 

 cleavage ; before invagination has begun ( X 48). 



Figs. 49-51. Horizontal sections through egg shown in Fig. 37, in planes 

 49-49, 50-50, 51-51. 



[Outlines drawn with the camera. Figs. 34-45, X 20 ; Figs. 46-51, X 48.] 



