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318 tonic spasm of the same kind as that already alluded to in the case of Tiaropsis polydiademata. Now, it is a remarkable fact that into whatever form the bell of this medusa is cut—say, for instance, into the form of a long ribbon—whenever a locomotor contraction is started by stimulating any part of the general nervo-muscular sheet, it will pass all through that sheet, from end to end of the ribbon, in the form of an ordinary or gentle contractile wave. On the other hand, whenever a spasmodic contraction is started in the nervo-muscular sheet by stimulating any of the marginal ganglia, it will pass all through that sheet, from end to end of the ribbon, in the form of a spasmodic or violent contractile wave. Hence the muscular fibres of this medusa are capable of liberating this energy in either of two very different ways; and whenever some of them liberate their energy in one of these two ways, they determine that all the other fibres in the nervo-muscular sheet shall do the same. So that we may adopt a far-fetched but convenient simile, and liken the muscular fibres in this medusa to the fibres in a mass of gun-cotton. For in a mass of gun-cotton the fibres are likewise able to liberate their energy in either of two very different ways—viz., either by burning in quiet flame when they are simply ignited, or by exploding in a violent manner when they are detonated, as by a percussion-cap. And both in the case of the muscle-fibres of Staurophora and the cotton-fibres of gun-cotton, whenever any one of the whole number is made by appropriate stimulation (i. e., muscular stimulation or ignition) to liberate its energy in a quiet manner, then all the other fibres in the mass do the same; whereas, if any one of the whole number is made by another appropriate stimulation (i. e., ganglionic stimulation or detonation) to liberate its energy in a violent manner, then all the other fibres in the mass do the same. Now why the ganglia of this medusa should thus act as detonators to the muscular fibres, and why, if they do, the muscular fibres should be capable of two such different kinds of response—these are questions quite novel in physiology, and as such I will not endeavor to answer them.

—As my space is now very nearly exhausted, I will conclude this article by very briefly stating the general results of a large number of observations concerning the action of various nerve-poisons on the Medusæ. It is easy to see that this is an important branch of the inquiry on which I am engaged; for in the nerve-poisons we have, as it were, so many tests whereby to ascertain whether nerve-tissue, where it first appears upon the scene of life, is of the same essential character, as to its various functions, as is the nerve-tissue of higher animals.

Chloroform, ether, morphia, etc., all exert their anæsthesiating influence on the Medusæ quite as decidedly as they do on the higher animals. Soon after a few drops of the anæsthetic have been added to the water in which the Medusæ are contained, the swimming motions of the latter become progressively slower and feebler, until in a minute or two