If one of the very large cells be taken from the ganglion of a living mollusc, and be gently pressed till it bursts, the discharged contents will be seen to be of a hyaline viscid substance, with fine granules but no trace of fibres. Yet we must not rashly generalize from this, and declare that in the vertebrate cells the substance is not also fibrillated. As a good deal of speculation rests on the assumption of the fibrillated cell-contents, I have thought it worth while to note the uncertainty which hovers round it. 122. Among the uncertainties must be reckoned the question as to the cell-processes. The existence of apolar and unipolar cells is flatly denied by many writers, who assert that the appearances are due to the fragility of the processes. Fragile the processes are, and evidence of their having been broken off meet us in every preparation; but the denial of apolar and unipolar cells seems to me only an example of the tendency to substitute hypothesis for observation (§ 114). The “postulate” which some seem to regard as a “necessity of thought” that every nerve-cell shall have at least two fibres, one ingoing, the other outgoing, is allowed to override the plain evidence.[143] It originated in the fact first noticed by Wagner and Charles Robin that certain cells in the spinal ganglia of fishes are bipolar. The fact was rapidly generalized, in spite of its not being verified in _other_ places; the generalization was accepted because (by a strange process of reasoning running counter to all physiological knowledge) it was thought to furnish an elementary illustration of the reflex process. As the centre had its ingoing and outgoing nerve, so the cell was held to be a centre “writ small,” and required its two fibres, No one paused to ask, how a cell placed in the _track_ of an ingoing nerve could fulfil this office of a reflex centre; no one supposed that the portion of the sensory fibre which continued its course, after the interruption of the cell, was a motor fibre. What does Observation teach? It teaches that at first all nerve-cells are apolar. Even in the cortex of the cerebrum, where (unless we include the nuclei and grain-like corpuscles under cells) all the cells are finally multipolar, there is not one which has a process, up to the seventh or eighth day of incubation (in the chick); from that day, and onwards, cells with one process appear; later on, cells with two, and later still, with three. By this time all the apolar cells have disappeared. They may therefore be regarded as cells in their infancy. However that may be, we must accept the fact that apolar cells exist; whether they can co-operate in neural functions, is a question which must be decided after the mode of operation of cells is placed beyond a doubt.