ee 
BLOOD-VASCULAR SYSTEM, ETC., OF AMIURUS CATUS. 44] 
supraclavicle and the transverse process of the fourth vertebra. 
From this thick rounded dorsal portion it gradually thins out ven- 
trally and curves backward upon the surface of the air-bladder, thus 
becoming convex upon the anterior, and concave upon the posterior 
surface. The aponeurotic membrane, which covers it anteriorly, 
forms a strong capsule for it by sending its shining fibres into the 
peritoneum, which stretches backwards along the cesophagus so as to 
cover it ventrally, and, passing over its dorsal surface, is attached to 
the transverse process of the fourth vertebra, and then continued 
downwards between the air-bladder and the gland. The lateral lobes 
of the liver insert themselves between the membrane covering the 
’ head-kidney and the body wall. It is also covered by a delicate con- 
nective tissue membrane of its own, well supplied with blood-vessels. 
The artery to the head-kidney referred to above enters the connect- 
ing portion and divides into two branches, one to each half of the 
gland. Judging from their size they cannot do more than supply 
nourishment to the gland substance, while the vein from the body 
wall which enters at the outer dorsal angle furnishes the blood to be 
acted upon. The veins which drain the blood into the posterior car- 
dinals appear out of all proportion in number and size to the afferent 
vessels. More than twenty openings of these vessels, many of them 
quite large, can be counted on the inner surface of the right cardinal. 
The frame work of the gland consists of a finely reticulate con- 
nective tissue. The interspaces are in places filled with the lymphoid 
cells of the glandular pulp, and at others serve as blood spaces. The 
areas occupied by the lymphoid t:ssue and the blood spaces are about 
equal. (Pl. VIII, Fig. 9.) Brown pigment patches, exactly similar 
to those seen, but in greater abundance in the spleen and kidney, 
are irregularly scattered through its substance, and increase with the 
age of the gland. 
The change from the kidney to the lymphoid structure! was not 
completed in the youngest specimens of which sections were cut, for 
a few epithelial lined tubules remained in the neighbourhood of the 
cardinal veins. A section through the head-kidney, near its anterior 
surface, showing these has been drawn by Prof. Wright. (Pl. IV., 
Fig. 14, 2k.) The figure is reversed and the large right cardinal 
vein appears on the left, near the centre of the lobe, surrounded 
by the tubuli. 
1 Balfour—Quat. Jour. Mic. Se., N.S., Vol. XXII, Jan., 1882. 
