'^o^u^lL.'fi^ITilS'] ^/ Ovum of the Pike, 197 
where the intestine turns downwards through the tail membrane to 
the aperture of exit (i). At the bend (k) the vein crosses the intes- 
tine, and becomes placed underneath it, until it reaches the poste- 
rior tapering end of the yelk-bag (I, the intestine, traceable upwards 
to the mouth, the letters ^, e, and h being placed on it ; and down- 
wards by k to its termination, i ; m, the posterior end of the yelk- 
bag). During its passage from h to m, it receives, first, a large vein 
at k, which can be traced forwards (mouthwards), lying just below 
the aorta, and which receives the veins corresponding to the dorsal 
arteries shown in Fig. 25 ; from this vein pass two or three com- 
munications to the cardinal vein, higher up than the principal 
junction at k, as marked at n; 2ndly, a vein, seen at w, which 
turns round the tapering extremity of the yelk-bag, and joins the 
main vein. 
These two veins would appear to return venous blood into the 
cardinal vein from the body below the point /. The cardinal vein 
thus formed of three conjoined currents passes along the ventral 
border of the yelk-bag, the blood as yet spreading but httle over the 
sides or general surface ; it passes then in the median line around 
the yelk-bag until it reaches its junction with the mouth (o), when 
it meets current a, then turns inwards and meets current y8. This 
latter current is the return blood from the head (muzzle to /), and 
is formed as follows : — The superficial veins of the head converge 
from all points to two large veins, which pass one above and the 
other below the ear (seen above and below d) ; into the one above 
the ear enters a third, which appears to come from the deep parts 
of the head. The vein above and that below at length unite 
behind the ear, and the resulting vein crosses the aortic circle and 
the intestine, and finally runs out by a round aperture into the 
auricular sinus (^). This is the case on the left side ; on the right 
side, after the blood has reached the surface of the yelk-bag it turns 
and goes underneath the head ; reaching the point g, the right and 
left currents run parallel, a clear interval remaining between them, 
until they reach the heart, the two forming current fi. 
A portion of the blood from the right cardinal vein passes along 
the right side of the yelk-bag to the muzzle, and there crosses over 
to the left by the junction of the muzzle and yelk-bag, forming 
current a (seen at o). The remainder runs downwards to join the 
right-side current from the head, which passes under the head to gr. 
The current from the left cardinal vein meets current a. at the 
muzzle of the fish, passes onwards to the heart, and at the entrance 
to the auricle meets current ^, coming from a diametrically opposite 
point ; the two run into the auricle by the side nearest to each, 
mingle, and enter the ventricle — the place w^hence we started. 
In the eye is seen the iris (s), a broad band surrounding a round 
space, a line where two extremities of the band have united being 
