OUTGROWTH OF THE XERVE FIBER 831 
denied by the adherents of Hensen's theory. Early proto- 
plasmic connections have been observed by them, and by assum- 
ing these to be primary, as Kerr has done in the case of the motor 
roots of Lepidosiren, or at least by not realizing that connections 
of that kind are established by the outflowing of the protoplasm 
of the neuroblasts, they have been advanced as evidence in sup- 
port of the protoplasmic bridge theor3\ Held and Paton, in their 
recent work, have emphasized the differentiation phenomena, and 
have totally failed to recognize the importance of the proto- 
plasmic movement which precedes. This is of course a natural 
consequence of relying entirel}^ upon specific staining methods. 
Means of demonstrating neurofibrillae at the earliest possible 
moment were sought and found, and though undoubtedly one 
result has been a great advance in our knowledge of the processes 
of neurofibrillation, it is equally without doubt that another 
result has been the production of a one-sided view of the develop- 
ment of the nervous system. This is exemplified in the opening 
sentence (following the historical sketch) of Held's monograph 
where one reads^^ ^'Bei der Frage nach der Entwicklung des Ner- 
vengewebes handelt es sich um den Nachweis der ersten histolo- 
gischen Characteristika des spaterhin so eigentlimlich ausgepriig- 
ten und im Tierkorper weit verbreiteten Nervengewebes" (mean- 
ing by this the neurofibrillar substance). Held, it is true, holds 
that the fibrillar substance is formed by the neuroblasts of His, 
and he describes the pushing out of the fibrillae from the center 
into the peripheral protoplasmic net work ; he also enters upon a 
discussion of the influences which bring about the nervous con- 
nections found in the adult organism,^" so that there is a close 
15 Op. ciL, p. 10. 
1^ Held recognizes a number of principles in the outgrowth of the fibrillar sub- 
stance which are closely similar to those stated by His and followed here, as, for 
instance, "das Prinzip der Achsenstellung" and "das Prinzip der Wegstrecke" 
(op. cit.,p. 278) ; and in his reference to chemotaxis (p. 148), and to the "Prinzip der 
Auswahl" (p. 270), Held's views lean strongly toward those of Ramon y Cajal. 
It must be borne in mind, however, that in all these cases Held refers solely to the 
movement of the fibrillar substance within the preformed reticular protoplasm, 
instead of recognizing that it is a mass of undifferentiated neuroblastic protoplasm 
that moves, and that this afterwards forms the neurofibrillae within itself by dif- 
ferentiation. 
