Miscellaneous. 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 Vorticelloi in the most simple condition which 

 it is possible to imagine. In many Invert ebrata an entire muscle is 

 often represented by a single primitive bundle ; in the Rotifera iso- 

 lated fibrillse 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 has 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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