DEVELOPMENT AND LIFE-HISTORIES OF TELEOSTEAN FISHES. 877 



the blood returning by two main branches — the afferent trunks from the liver carrying a 

 stream downward posteriorly and joining the posterior division, the other great branch 

 receiving its supply from the opposite side (PL XX. figs. 4 and 5). Considerable gaps, 

 as regards the larger trunks, occur on each side of the vitelline vein and below its branches 

 at this stage, but examples somewhat differ from each other in this respect. These 

 trunks are all, even the smallest, of comparatively large calibre, and appear in ordinary 

 views to be hollowed out of the yolk, and without the distinct walls of typical venous 

 trunks. The vessels frequently anastomose with each other, and their general direction 

 is downward and forward. Some of the upper twigs (in larvae of 22nd February) pass 

 rapidly across the yolk-sac to join the main vein, above the oil-globule. When the 

 fish is in a dying condition the current becomes less swift, and frequently recoils in the 

 vessels, but especially in the great vein. On the left side (PL XX. fig. 2) a great trunk 

 from the liver courses along the anterior hepatic curvature, while several smaller but 

 still considerable trunks issue from the same organ posteriorly, and rapidly break up into 

 many branches, forming a complex network over the posterior half of the sac. Their 

 terminal branches join a large and nearly horizontal trunk, which slants slightly upward 

 and forward to join the vein. The divergence of this arrangement from such a species 

 as represented in PL XV. fig. 2, from ova resembling those of Montagu's sucker, is 

 marked, the vessels in the latter being few and short, and having a comparatively 

 straight course. 



About a month later (PL XXI. fig. 2) the complexity of the circulation on the left 

 side has increased. The anterior vessel of the series issuing from the liver, which curves 

 downward and forward — branching as it goes, has become much larger. 



On 1st April, again (about 5 weeks later), the chief change since the former period is 

 the great size of the anterior trunk (marked a, PL XXI. fig. 2) and its shorter course. 

 The vessels to the right (that is the posterior vessels) are diminished, and they have a 

 decided slope to the front. The slope, however, is much less marked than on the right 

 side. In the most advanced forms at this time (PL XXIV. fig. 7) the alteration in the 

 direction and size of the vessels of the yolk is remarkable. Thus, on the right side, the 

 main part of the blood is conveyed by a large trunk passing to the posterior border of 

 the liver — slightly downward and forward (though the course may vary) into the great 

 vitelline vein, a little below the heart. This blood does not, therefore, pass over the sac. 

 Some of the vessels of the yolk seem to have diminished in size. The great trunk just 

 alluded to is twice the size of that in an example in which the yolk is still very large 

 (i.e., a younger specimen), yet each, though so unequally advanced, may have emerged 

 from the ovum almost at the same time. Of course, the diminution of the yolk-mass 

 enables the larval-fish to swim more readily through the water. It must be noted that 

 the direction of the trunks detailed above may, as indicated, vary considerably, for in one 

 example two large trunks issued from the front of the liver, then rapidly curved toward 

 the anterior border and joined the efferent vein. The rapidity of the current in these 

 two main trunks is in contrast with the steady and slow current in the branches covering 



