BLOOD-VASCULAR SYSTEM, ETC., OF AMIURUS CATUS. 441 



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 oesophagus 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 tissue and the blood spaces are about 

 equal. (PI. 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 1 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. (PI. IV., 

 Fig. 14, hk.) The figure is reversed and the large right cardinal 

 vein appears on the left, near the centre of the lobe, surrounded 

 by the tubuli. 



i Balfour— Quat. Jour. Mic. So-., N.S., Vol. XXII., Jan., 1882. 



