104 Walter E. Dandy. 
EXPLANATION OF PLATES. 
PLATE II (F ies. 8-11). 
Tic. 8. Section 177, « 25. Outline of section to show size of the sinus 
formed by union of umbilical veins; V, Umbilical venous sinus (from union 
of the umbilical veins); All, Allantois, shown in two places, the lower is 
before division, the upper is terminus of long branch; Ch, Chorion; Vi, 
Chorionic villus, showing syncytial bud; U, Umbilical artery, shown in two 
places below, before union to form umbilical arterial sinus, and above, tip 
of sinus and large branches. 
Fic. 9. Section 188, % 25. Outline of section to show size of sinus formed 
from union of umbilical arteries. U, Umbilical arterial sinus; All, The 
terminus of the short branch of the allantois; Ca, Capillaries and small 
branches of sinus in chorion; Ch, Chorionic Membrane; Vi, Chorionic villus, 
showing capillary entering. 
Fic. 10. > 525. Capillaries from chorion, showing apparent formation 
of blood corpuscles from endothelium of capillaries. 
Fig. 11. Reconstruction of ccolom, showing relation to somites; Arabic 
numbers on side represent the numbers of sections; Roman numerals in 
center represent the paired somites; P.C., Pericardial celom; Pl, Pleural 
ceelom; Coe, Peritoneal celom; E.C., External Communication of the ccelom ; 
Pr, Pronephros; Ht, Projection of the heart in the pericardial cavity; X, 
Outer limit of body wall; Mes, Paraxial mesoblast ; Br.M., Bridge of meso- 
dermal tissue extending across the mesodermal slit; Pr.S., Primitive streak. 
