452 ARTHUR ROBINSON. 
EXPLANATION OF PLATES XXIII—XXVII, 
Illustrating Mr. Arthur Robinson’s paper on “ Observations 
upon the Development of the Segmentation Cavity, the 
Archenteron, the Germinal Layers, and the Amnion in 
Mammals.” 
Alphabetical List of Reference Letters for all Figures. 
AA, Allantoie artery. AFH. Head amnion fold. AFT. Tail amnion 
foid. 4Z. Allantois. d/. Amnion. AMC, Amnion cavity. AMP. Pro- 
amnion. AV. Anal membrane. BMP. Bucco-pharyngeal membrane. CAS. 
Caudal side of embryonic cylinder. CD, Chorda dorsalis, CHS. Cephalic 
side of embryonic cylinder. CHY. Chorda hypoblast. CO#. Celom. D. 
Distal or anti-mesometrial. DA. Dorsal aorta. DWT. Distal wall of tropho- 
blast. #. Germinal epiblast. HC. Cavity of epiblast. HD. Hctoderm. HY. 
Hypoblast. AY#, Uninvaginated or external hypoblast. HY. Hypoblast of 
ventral wall of fore-gut. HYZ. Invaginated or internal hypoblast. 2. Meso- 
blast. MY. Blood islets. WC. Neurenteric canal. NHC. Neural canal. 
P. Proximal or mesometrial. PAJ/. Paraxial mesoblast. PC. Pericardial 
cavity. PCM. Precephalic mesoblast. PG. Primitive groove. PS. 
Primitive streak. SC. Segmentation cavity. S27. Somatapleure mesoblast. 
SP. Splanchnopleure mesoblast. 7. Trophoblast. 7C. Secondary cavity of 
trophoblast. 7C.’ Primary cavity of trophoblast. 7D. Distal portion of 
trophoblast. 7D. Distal wall of trophoblast cavity. Z'P. Proximal portion 
of trophoblast. VA. Vitelline artery. VC. Vitelline cavity. 
PLATE XXIII— 
Fic. 1.—Mesial section of the ovum of a rat at the fourth day. x 566. 
Fig. 2.—Section [fifth of eight] of the ovum of a rat at about the fifth 
day. x 566, 
Fic. 3.—Section [fifth of eight] of another ovum from the same uterus 
as that represented in Fig. 2. x 566. 
“Fic. 4.—Longitudinal section [sixth of eleven] of the ovum of a mouse. 
at about the end of the fifth or in the early part of the sixth day. x 566. 
Fic. 5.—Longitudinal section [sixth of nine] of the ovum of a mouse at 
the sixth day. x 566. 
Fic. 6.—Mesial longitudinal section of the ovum of a mouse at the sixth 
day. ™X 566. 
