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This increase of complexity is due largely to the more distinct introduction of time. Sensations remain in the memory, and the experiences, also, which have arisen under them; they thus serve to combine actions through long periods. Actions and sensations united by the mediation of consciousness constitute the associative life. By the intervention of reason, still broader areas and longer periods may be included, and the complexity of responsive movement becomes incomparably greater. These combinations are those of the rational life. These forms of life do not exist by exclusion, but by the inclusion of the lower under the higher; by the building of the higher on the lower.

Lesson 89 - 4. Various forms of a nervous system - p.375

4. The simplest form of the nervous system is that of nerves united in a single ganglion. An example of this is seen in an Ascidian, belonging to the class of Mollusks, A first step of combination is found in the union of several proximately equal ganglia, each with its own nerves, to each other by other nerves. Each stimulus thus affects not simply its own ganglion, but other ganglia, and the reaction is proportionately extended. The star-fish and the sea urchin, belonging to the Radiates, present examples. In the star-fish, a circle of ganglia are gathered about the central opening, each ganglion being also connected by nerves with the ray to which it corresponds. Thus the stimuli of any ray act on all rays. A third form of the nervous system found in Mollusks, as the fresh- water-clam and the oyster, consists of several unequal ganglia, somewhat irregularly distributed through the body, in connection with leading functions, and united to each other by filaments or by cords. Thus the oyster has a large posterior ganglion closely connected with the great adductor muscle, with the mantle, and with the gills. It has two much smaller ganglia, situated on either side of the mouth and! united above and below it.