18 H. V. NEAL 



('04) and Braus ('05) have added to the Hensen hypothesis the 

 assumption of an original and unchangeable connection of motor 

 nerve and muscle. 



Held ('09) suggests that the assumption of primary — ab initio 

 — connectJon between muscle and nerve is not an essential part 

 of the Hensen hypothesis. With this view, however, Hensen 

 ('03) does not seem to agree. Hensen states his hypothesis in 

 his Vorrede as follows: ''Nervous connections are not established 

 through the free outgrowth of the nerves in the embryo, but 

 central and peripheral organs remain in connection with each 

 other from the time of their formation (Sonderung) until the 

 complete differentiation of the nervous trunks." 



2. The second theory is that advanced by Schwann ('39) and 

 later revived by Balfour ('77) as the cell-chain hypothesis, accord- 

 ing to which the nerve fiber arises from the union of a series or 

 chain of primary cells, which later accompany the neuraxon as 

 the so-called Schwann's or neurilemma cells. According to this 

 hypothesis nerve fibers are formed by the fusion of primary 

 cells, whose nuclei become the nuclei of the differentiated fiber, 

 so that the nerve fibers are in consequence multicellular in origin. 

 This theory has been supported by Marshall ('78), VanWijhe 

 ('82, '86, '89), Beard ('85, '88, '92), Miss Piatt ('94, '96), Sedg- 

 wick (94, with some modification), Hoffmann ('96), Kupffer ('90, 

 '91, '94), Rafaelle ('00), Bethe ('00-'07, with modifications), 

 Brachet ('05, '07), Cohn ('05, '06, '07), Oscar Schultze ('04-'07). 



According to the cell-chain hypothesis, the peripheral nerve 

 fiber is the common product of a chain of cells, on the end of 

 which, in the case of a motor nerve, or in an intermediate 

 position, in the case of a sensory nerve — the larger cell forming 

 the ganglion cell is situated. The cell chain not only forms the 

 ganglion cell but also the cells of the neurilemma sheath, which 

 are not merely sheath cells but also the cells that produce the 

 fiber — as nerve-fiber cells or 'neurocytes' (Kupffer), 'nerve-cells' 

 (Bethe and Apathy) or 'neuroblasts' (O. Schultze). The nerve 

 fiber is thus an elongated mosaic consisting of a series of cells, 

 each cell of which has added to what another cell before it has 

 formed, and has continued into the following cell. Bethe ('00- 



