DEVELOPMENT AND LIFE-HISTORIES OF TELEOSTEAN FISHES. 883 
condition is precisely similar to that in the young Clupeoid, 4 inch in length, the heart 
being saccular, and consisting of 3 or 4 layers of cells, many of them very round and 
prominent. The endothelium is, however, flattened. The cells in the wolf-fish project 
internally, so as to occupy a considerable portion of the central area, but much less now 
than afterwards. The bulbus in contraction at this stage is nearly cylindrical, its central 
cavity being evident just above the valves, and it is on minute examination seen to be 
composed of fibres and cells. The auricle has a cellular wall, the cells apparently being 
also fibre-cells, and the wall is now better defined externally, as if from more continuous 
fibrillation, this differentiation of a stronger outer layer being also observed in the young 
Clupeoid at the stage just referred to. 
As the organ attains greater complexity, the ventricle largely assumes a reticulated 
appearance from the vascular ramifications of its walls (Pl. XXV. fig. 1, ven), the whole 
being in many sections not unlike a fibrous sponge—a condition characteristic of the heart 
in the adult. This structure is also shown in the young Clupeoid, when 3; inch long— 
small spaces being formed in the loose saccular walls, which, as in the shghtly younger 
stage, are studded with large scattered nuclei. Quite different is the structure of the ven- 
tricular walls of the post-larval goby, >; inch long, the spaces being formed in very dense 
and thick tissue. The walls of the auricle in Anarrhichas, as in Clupea, Gobius, and 
others when + inch long, consist of a thin muscular layer lined by endothelium. In the 
most advanced stage of the wolf-fish (20th June) the two valves at the base of the bulbus 
are well defined. The reticulations of the conical ventricle are much finer and more num- 
erous, and the fibres more distinct. With the exception of the central chamber, which 
occupies about a fourth of the thickness towards the base, the whole organ is reticulated in 
this manner, and the blood passes into the reticulations. So accurately do the auriculo- 
ventricular valves close that in the preparation a thick column of blood projects into the 
auricle, the mass being covered by a tense membranous layer, apparently valvular. 
The heart in the young salmon, at thirteen and forty-five days respectively, presents 
corresponding features to that of the wolf-fish, though the nuclei in the muscle-cells are 
much more distinct both in the early and later stages. 
When fully developed the circulation in the larval wolf-fish presents, in regard to the 
vertical or what may be called the vertebral branches of the aorta, a similar arrangement to 
that in the salmon, which has about 26 or 27 of them. These somewhat differ in the latter 
fish in the several parts of the body. Thus the anterior branches (Pl. XXVIII. fig. 2, a) 
course straight up from the aorta to the middle of the trunk, then give off the oblique 
twigs (b) which proceed downward and backward so as to form the oblique lines so notice- 
able in the living fish. They alternate with venous trunks (¢ and d) having the same 
direction. These arterial twigs admit only a single line of corpuscles, which proceed with 
great rapidity, and join the respective veins (c), and then by the larger trunk (d) debouch 
into the cardinal. Beyond the oblique arterial branches just noted the vessels course 
upward and slightly backward to the border of the muscle-plates, and give off various twigs 
before terminating in the venous radicles. Posteriorly the oblique branches appear to 
