Albert C. Eycleshymer and James Meredith Wilson 161 
PLATE III. 
Fic. 31. Meridional section of egg about fifty-five hours after fertilization, 
showing thickening of ectoblast to form head of embryo. 
Fig. 32. Sagittal section of an embryo some sixty hours after fertilization 
showing further differentiation of embryo. 
Fic. 33. Sagittal section of an embryo about sixty-three hours after fertili- 
zation, showing further growth of embryo, the obliteration of the segmenta- 
tion cavity, the extension of the gastral cavity, the reduction of yolk plug. 
Fic. 34. Sagittal section of posterior end of embryo about seventy hours 
after fertilization, showing the closure of the blastopore. 
Fig. 35. Transverse section through the blastopore of an embryo in same 
stage as above. 
Fics. 36, 37. Sagittal section of embryo about seventy-two hours after fer- 
tilization. The anterior portion of the embryo is shown in Fig. 36, while the 
posterior portion is shown in Fig. 37. 
Fic. 38. Oblique section of an embryo seventy-five hours after fertilization 
showing the thickenings which later form the optic vesicles. 
Fic. 39. Transverse section of an embryo of same age passing through the 
posterior portion of the hind brain. 
Fic. 40. Transverse section of same embryo at the level of Kupffer’s vesicle. 
Fic. 41. Transverse section of an embryo of same age, showing deep neural 
trench and posterior end of notochord. 
Fic. 42. Sagittal section of head end of embryo about ninety-five hours after 
fertilization, showing divisions of brain, notochord, gut, adhesive organs, and 
the peculiar invagination of the ectoblast just anterior to the fore-brain. 
PLATE IV. 
Fic. 43. Transverse section through embryo of same age at the level of 
the adhesive organs. 
Fic. 44. Transverse sections of same embryo at level of optic vesicles. 
Fic. 45. Transverse section of same embryo at level of anterior margin of 
medulia.. 
Fic. 46. Transverse section of same embryo through the region of the 
auditory vesicles, showing the first appearance of pronephric duct and hypo- 
chorda. 
Fic. 47. Transverse section of same embryo at the level of last protover- 
tebra. 
Fic. 48. Sagittal section of embryo one hundred and ten hours after fertili- 
zation, showing the beginning of the epiphysis and infundibulum, also the 
median portion of the adhesive organs and the heart. 
Fic. 49. Transverse section of an embryo one hundred and twenty-five hours 
after fertilization taken just in front of the region of adhesive organs showing 
heart, gut and coelom. 
Fic. 50.. Obliquely transverse section of an embryo of same stage passing 
through the anterior margin of the adhesive organs on the one side and the 
optic stalk and vesicle on the other, showing the approximation of the layers 
of the splachnopleure to form the heart. ; 
