Monthly Mlcroscopkan 
Journal, Oct. 1, 1869. J 
of the Ovum of the Pike. 
199 
with great velocity througli the winding ways is a most beautiful 
object to witness. 
2\th Ap%l, 11th day. — In the fully developed state there are 
five bony arches^ called branchial arches ; of the four anterior of 
these each one supports a branchial artery ; these four branchial 
arteries with the first trunk extending from the heart to the aortic 
circle, constitute the five arterial arches which are given off on each 
side in the embryo. The second arterial arch, or the first branchial 
artery, is much increased in diameter, being now as wide a vessel 
as the first arterial arch; two rudimental branchial bones stretch 
completely across the branchial region ; two others are seen poste- 
rior to the first two, and as yet very small. 
The circulation of blood over the yelk-sac is more extensively 
ramified to-day than it was yesterday. Other changes are occurring 
in the vein mentioned as passing from g to m (Fig. 39), but as the 
description would be uninteresting to the general reader, I omit it. 
2bth April, 12th day. — Slender, well-defined vessels are in pro- 
cess of formation in the membranous expansion around the caudal 
termination (tail-end) of the fish. They frequently join each other, 
but do not communicate with any vessel from the heart, being- 
isolated and bloodless. This shows that blood-vessels are laid down, 
as it were, and grow independently of any connection with the 
heart. Vessels are also shooting out from the side of the bony axis 
of the tail, in a direction suitable for meeting the isolated ones 
mentioned. The branchial arches now bend more decidedly, the 
convexity being towards the tail. The tail membrane now shows a 
deep cleft on its dorsal borders, indicating the approaching forma- 
tion of the dorsal fin (u). Pigment cells are beginning to show 
themselves on the parietes of the body. 
In a fish which had been put into shallow water, under a cover, 
and which had exhausted apparently all the contained oxygen of 
the water, the heart's action ceased. The blood ceasing to be im- 
pelled forwards from the auricle, that contained in the aortic circle 
flowed in a reverse direction, backwards. This was interesting, as 
showing the elastic recoil of the artery. But when by means of 
the branchial arteries this aortic blood had again reached the heart, 
it passed completely through it until it reached the auricular sinus. 
Arrived there, it immediately reverses its course again, enters the 
heart, causes the heart's pulsation again to take place, and by that 
means again reaches the branchial arteries and the aorta. I suppose 
that the blood, having reached this spot, was in a better position for 
aeration than elsewhere, and therefore more resembled the natural 
stimulus to the heart's action, as this very strange oscillatory action 
was repeated many times, the whole lasting some few minutes. 
26th A]r>ril, 13th day. — I observed four well-marked branchial 
arches springing from their centre, the hyoid bone ; and in addition 
