AND ON THE CLASSIFICATION OF FISH. 541 
portion of the artery ; but immediately on the contraction of the 
bulb, the blood would return from the artery, where it is sub- 
jected to the pressure of the whole arterial system, and would 
again fill the bulb as far as the valves in the ventricle ; in short, 
the muscular bulb would here be useless as a pulsatory portion of 
the heart. After these reflections I was sufficiently interested 
to observe the heart of the first osseous fish which came in my 
way whilst in vital activity. I then immediately found that the so- 
called muscular arterial bulb of the osseous fishes effects no pul- 
sation, and that it differs in this completely from the extremely 
active bulbus aorte of the Batrachia. On the heart of a Cyprinus, 
Salmo, Pike, we observe, that as soon as the pulsation of the 
ventricle succeeds that of the auricle, the bulb and the arteries 
continued from it are powerfully dilated by the injected blood ; 
thence, until the next contraction of the ventricle, the bulb and 
artery again gradually contract,and this contraction occurs in the 
bulb exactly in the same manner as in the arteries, only more 
powerfully. It is also impossible by mechanical, electrical or 
chemical irritation to make the bulb, either when empty or cut 
into pieces, pulsate or contract. 
The next step is to compare the minute structure of the mus- 
cular substance of the bulb in the Plagiostomi and Ganoids with 
that of the osseous fishes. We then find that the muscle of the 
arterial trunk of the Plagiostomi and Ganoids consists of trans- 
versely striated muscular fibres having the same structure as in 
the ventricle and auricle. On the other hand, the substance of 
the bulb in the osseous fishes exhibits no trace of the trans- 
versely striated fibres of the heart, but consists of mere bundles 
of delicate fibres, which have not the most remote resemblance 
to the former muscular fibres. The substance, in a gradually 
attenuated form, is continued into a similar tunic of the artery, 
which is continued over the entire ramification of the gill-artery 
and again appears in the gill-veins. The bundles of this layer 
and those of the bulb, may be compared to those which Henle 
discovered in the arterial tunic, consisting of annular fibres, and 
in which he placed the seat of organic contraction. The bulb, 
the walls of which in Samo are about eight times as thick as the 
walls of the gill-artery, would then constitute a cardiac dilata- 
tion of a tonic layer. But our bundles are very elastic; and it 
is at present problematical whether the bulb possesses organic 
contractility. In the Sharks, Rays, Sturgeons, or Ganoids, 
