. Electro-physiology . -\ ably in the two cases. AYliile in the cells of the adductor and pedal muscles the formative plasma is insignificant in comparison with the contractile substance, in the cardiac and masticatory muscles it preponderates. Knoll, who first investigated these differences systematically, used the terms a-plasmic (" clear ") and jilt/tune ("dark") to designate the two cases, the cells of the cardiac and masticatory muscles being by far the richest in protoplasm, and less transparent. These comparative investiga- tions prove beyond doubt that the structura
. Electro-physiology . -\ ably in the two cases. AYliile in the cells of the adductor and pedal muscles the formative plasma is insignificant in comparison with the contractile substance, in the cardiac and masticatory muscles it preponderates. Knoll, who first investigated these differences systematically, used the terms a-plasmic (" clear ") and jilt/tune ("dark") to designate the two cases, the cells of the cardiac and masticatory muscles being by far the richest in protoplasm, and less transparent. These comparative investiga- tions prove beyond doubt that the structural ratio is, like cross-striation, of functional significance, as also appears from obser- vations on the muscles of higher animals to be discussed below. The cardiac and buccal muscles have obviously more work, and more persistent work, to do than the adductor muscle of mol- luscs or the pedal muscle of snails, which are used leSS ireC^liently, and Since pIG_ 10.—Transverse section of muscle-cells of Mollusca. the formative plasma (Knoll.) «, Heart of Aplysia punctata; Z>, heart of Ai>liisin limacina : c, masticatory apparatus of Cari- Stands, as Will be shown, naria; d, longitudinal view of muscle-cells from in close relation with the buccal mass of ^ia,™ nutrition of the contractile substance, we can readily appreciate the proportions given. This theory is substantially confirmed by the " float" muscles of Carinaria. That portion of the foot which is used for floating, and is in constant movement, corresponds both in the cross- striation of the fibrils, and the abundance of its sarcoplasm, to the type of dark " plasmic" muscle-cells characteristic of the buccal and cardiac muscles of Mollusca. Along with the greater richness of sarcoplasm there is often a more or less definite coloration of the muscular elements. The cardiac and masti-
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