Scymnus brevipinna. 481 
of the one above; each large valve was about three lines 
square; when lying against the parietes they formed a con- 
tinuous line of prominent rough valves ; a most beautiful, and 
one would think, sufficient system. But as if this were not 
enough to prevent the reflux of blood, there is another stronger 
system immediately above it, consisting of three semilunar 
valves, nearly half an inch in depth, and set each upon a 
prominent fleshy columna, 2 of an inch in length, and j of 
an inch wide, rounded at each extremity, and fixed for its 
Whole length to the walls of the vessel; a semilunar valve 
over each longitudinal row of large valves. ‘This upper sys- 
tem of valves is just below the first branch given off to the 
branchize — the branchial artery gives off the first and second 
branches of each side close together, just at its origin from 
the bulb; an inch higher up, the third branch; two inches 
above this it bifurcates, almost at right angles ; each bifurca- 
tion runs about an inch, and then again bifurcates into the 
fourth and fifth branchial branches, the fifth being the small- 
est; the diameter of the main artery is $ an inch ; that of the 
branches, 4 of an inch. Müller (Op. citat. p. 191) states 
that the «bulb ” in the osseous fishes is no part of the active 
central organ of circulation, and does not pulsate as the 
t— while in the Selachi and Ganoids it acts as a true 
heart, or ventricular cavity, to propel the blood. | 
Müller gives no plate of the valves in the “bulb” of the 
Scymnus. His 4th fig, Pl. 5, represents them in a species of 
Lamna ; but their arrangement is different in the Scymnus: 
In the latter they appear more as in his 3d figure of the 2d 
P late, though the number of valves in each longitudinal row 
I5 less in our specimen. : 
From the branchial arteries the blood passes to the branchial 
veins, which ultimately unite above to form the “ aorta," cor- 
responding to this vessel in mammalia. T. 
‘Though the heart of fishes has but two cavities, we see 
‘at their circulating system is very different from that of the 
32 
