the whole blastoderm can be removed from the egg with much 

 greater ease than before. The head-fold has now become more 

 prominent than before. The nerve-tube, at first of uniform thick- 

 ness dilates anteriorly forming the first cerebral vesicle, and the 

 6econd and third cerebral vesicles successively form, the proto- 

 vertebrae increase rapidly, and soon the embryonic chick presents 

 the appearance of the embryo rabbit of nearly the same age. 



The alimentary canal commences as a cut de sac, closed in front 

 but widely open behind, situated below the anterior end of the 

 medullary tube. The heart originates also in the head-fold at 

 about the time the protovertebrse are formed, and the rudiment is 

 situated below the fore gut or rudiment of the alimentary canal : 

 by the end of the first half of the second day it is flask-shaped, 

 with a slight bend to the right. " Soon after its formation the 

 heart begins to beat, its at first slow and rare pulsations beginning 

 at the venous and passing on to the arterial end." Its movements 

 begin before the cells of which it is composed are differentiated 

 into muscle or nerve-cells. To provide channels for the fluid 

 pressed out by the contractions of the heart, the heart divides into 

 the two primitive aortse, and connects with other embrybnic tem- 

 porary arteries and veins. Meanwhile in the vascular area and 

 area pellncida, the arteries, capillaries and veins rapidly develop, 

 and blood disks arise as amoeba-like cells separating from the adja- 

 cent cell-mass of the mesoblast (middle germ-layer), while the 

 vessels are contemporaneously forming ; the red blood corpuscles 

 not being true cells, but nuclei. The first half of the second day 

 ends with the rise of the rudiment of the Wolffian duct. " It is 

 important to remember that the embryo of which we are now 

 speaking is simply a part of the whole germinal membrane, which 

 is gradually spreading over the surface of the yolk. It is impor- 

 tant also to bear in mind that all that part of the embryo which is 

 in front of the most anterior protovertebrae corresponds to the 

 future head, and the rest to the neck, body and tail. At this 



