33 6 LANGENBECK. 
EXPLANATION OF PLATE XXVIII. 
Fic. 46. Transverse section of the head region of an embryo shown in 
Fic. 47. Transverse section of the same egg about the middle of the ventral 
Fic. 48. Transverse section of the same egg nearer the posterior pole. 
Fic. 49. Transverse section of the head region of an egg of the first day. 
Fic. 50. Transverse section of an egg of the first day. 
Fic. 51. Part of a section of an egg of the first day. 
Fic. 52. Part of a section of an egg of the first day. 
Fic. 53. Transverse section passing through the center of the entodermal 
invagination. 
Fic. 54. Small portion of a sagittal section, showing the relative position of 
the dorsal organ and the entodermal invagination. 
Fic. 55. Sagittal section of an egg of the second day. 
Fic. 56. Oblique section of an egg of the stage represented in Fig. 38 passing 
through the region a-a. 
Fic. 57. Section of an egg of a stage between 38-42 passing through a-a, 
Fig. 42. 
Fic. 58. Section of the same egg passing through the line 4-d. 
Fic. 59. Section of an egg of the stage shown in Fig. 44, passing through the 
stomodaeum and proctodaeum and cut parallel to the line x—x, Fig. 44. 
Fic. 60. Another section of the egg shown in Fig. 59. 
Fic. 61. A section dorsal to the one shown in Fig. 60. 
Fic. 62. Thoracic portion of the second section beyond the one shown in 
Fig. 61. 
Fic. 63. Thoracic portion of the next section to the one shown in Fig. 62. 
Fic. 64. Thoracic section beyond the section shown in Fig. 63. 
