Miscellaneous. 3 147 
contraction of the muscle, but, on the contrary, the opposite state ; 
nevertheless it approaches the truth much more closely than the 
former. 
The observation of the phenomena of muscular contraction is 
presented to us in the Vorticelle in the most simple condition which 
it is possible to imagine. In many Invertebrata an entire muscle is 
often represented by a single primitive bundle; in the Rotifera iso- 
lated fibrillee form so many distinct muscles. The stalk of the 
Vorticella shows us the principal organ of locomotion of an animal 
composed of a single muscular fibrilla free in a canal in the centre 
of a perfectly transparent sheath, which allows us to see, with the 
greatest distinctness, all the changes which the contractile element 
undergoes during the states of activity and repose, of elongation and 
contraction. 
When the animal is at rest, the stalk is at its maximum of elonga- 
tion, and the body as far removed as possible from the point of 
attachment and refuge. The vibratile cilia alone are active, the body 
and the stalk remain perfectly immoveable. In this state the cen- 
tral filament of the stalk, the contractile fibrilla, is completely ex- 
tended; nevertheless it is never straight, but constantly presents a 
torsion in a very elongated spire, like a ribbon twisted round its 
longitudinal axis, and of which the appearance exactly resembles 
that of a spiral watch-spring fixed and strongly extended by the ex- 
tremities. As soon as any mechanical, electrical, thermic, or other 
excitant affects the animal, this elongated spiral, suddenly contract- 
ing upon itself, becomes transformed almost instantaneously into a 
perfectly regular spiral spring, with very close turns, which does not 
measure more than one-fifth of the length of the stalk in repose, 
and of which the transverse diameter las proportionately increased. 
This state generally persists only for a short time: the turns of the 
spring separating, it soon elongates, rather slowly, and the animal 
returns to its natural position. 
The shortening and elongation of the contractile organ are here 
manifestly due to the approximation and separation of a spiral spring; 
__ but to which of these two states belongs the action of elasticity? 
which of them shows us the muscular spring in its natural form, in 
its state of repose? Observation establishes, in the first place, this 
important fact—namely, that the spiral filament never appears in 
its extreme elongation except when the animal is alive and uninjured. 
As soon as the animal is killed, or detached from its stalk, sponta- 
neously or by violence, the turns of the spiral roll themselves up 
like a tendril, and remain in this state for an indefinite period ; the 
same is the case if the animal be suddenly killed by poison or by 
the elevation of the temperature to 104° or 113° F. 
It frequently happens, even during the life of the animal, that the 
contractile fibrilla breaks, and the continuity is broken between it 
and the body, the nutritive centre of the whole animal ; in this case, 
if the sheath be intact and continuous, the body, living and swimming 
by means of the vibratile cilia, drags along at its posterior part the 
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