XXVI. On the structure and formation of the so-called apolar, unipolar, and bipolar nerve-cells of the frog

Abstract

It is an opinion now very generally entertained by anatomists that in vertebrate and in certain invertebrate animals, there are in connexion with the nervous system apolar, unipolar, and multipolar, including bipolar cells. It is easy to demonstrate the presence of multipolar cells, but it is another matter altogether to prove that certain cells which seem to be apolar or unipolar are really of this nature. An observer is justified in asserting very positively the existence of that which he has himself distinctly seen and has shown to others; but it does not follow that he is correct in concluding that, because a fibre or other structure has not been seen by him in certain specimens, it therefore does not exist, for the actual exist­ence of a structure and its demonstration are two very different questions in minute anatomical inquiry. The one is a question of fact, no matter how it may be explained, or how many different interpretations may be offered of it. The other is but an infer­ence arrived at in the absence of evidence, and may result from imperfect means of observation, or want of due care on the part of the observer in preparing the specimen.