61 



The aflerenl vessel of the gill runs along the dorsal 

 wall of the branchial cone (PI. VIII, fig. 63), ventral to 

 the spleen, giving off alternate branches on its way, to the 

 alternating- internal ami external gill leaflets. Narrowing 

 down with the gill, it runs to its tip. The branch to the 

 leaflet runs in the supporting pillar, and, therefore, on 

 the side next to the gill cavity. Kunning along to the 

 ventral side of this cavity, it joins another venous vessel, 

 parallel to the main afferent vessel, and forming the 

 ventral wall of the gill cone (fig. 63). Again, each of 

 these vessels to the leaflets or primary elements of the 

 gill, gives off similarly alternating vessels to the 

 secondary elements of the gill (fig. 63, F 1 , 1^), and so 

 on. However, these vessels run along the outer edge of 

 the secondary, tertiary, &c, elements (fig. 62). On the 

 internal surface of the gill, where the leaflets do not 

 bear secondary elements all along their axis, the four 

 lowest folds receive blood from a common vessel (fig. 63). 

 The secondary vessels running up along the outer edge 

 of the corresponding folds, decrease in size and end on 

 the external surface of the gill, at the tip of the fold 

 (fig. 62). As there are eight series of gill elements, and 

 consequently eight series of vessels, the ultimate ones 

 are extremely fine. They open into a venous lacuna in 

 the gill filaments, and the blood which by now is in 

 great pari aerated and arterial, is gathered up again into 

 a network of arterial capillaries. Each accessory leaflet 

 receives blood from a vessel given off by the vein parallel 

 to the main afferent vessel, and described above. This 

 vessel runs along the outer surface of the accessory leaflet 

 and divides up exactly as do the branches to the secondary 

 elements of the gill (fig. 63). 



The finest arterial capillaries of the efferent vessels 

 are situated in the eighth elements of (he gill. Each 



