GROWTH OF TISSUES OF THE CHICK EMBRYO 75 



may apparently end without this enlargement. In many such 

 cases an enlargement is seen far back along the fibre (fig. 10). 

 This is apparently similar t.i the true end bulb. 



A discussion of the literature on nerve development and a fur- 

 ther comparison of these nerves with the nerves of the normal 

 chick embryo will not be taken up, but as far as I have been able 

 to determine, they conform in every detail to the nerves of the 

 embryo, as a comparison with Held's ('09) excellent figures show. 

 By a study of the stained serial sections of the culture, these fibres 

 can be definitely traced to" the neuroblasts as their cells of origin. 



The segmental arrangement characteristic of the embryonic 

 body has never been noted in nerves growing in culture from a 

 carefully isolated neural tube. Nerves appear very irregularly 

 along the pieces of transplanted tube and pass off irregularly into 

 the surrounding fibrin network. The character of the movement 

 and the course followed by a growing nerve suggests dependence 

 on the chemical condition of the media. The physical relations, 

 as shown in the architecture of the fibrin, apparently have little 

 influence aside from slight changes in the form of the larger bundles. 

 Nerves growing in a loose mesh or on the surface of the clot 

 spread out in a flat layer of fibrillae (fig. 7) which separate very 

 quickly into a large number of branches; these branches anasto- 

 mose frequently and form a network. In the dense fibrin network 

 they have a more compact rounded form. The possible existence 

 of attractive forces between other tissues and growing nerves has 

 been studied by transplantation of heart and myotome in close 

 proximity to a neural tube, but in only one of forty preparations 

 did the nerves enter the neighboring piece of tissue. Here the 

 fibre apparently was directed along a dense band of fibrin which 

 connected the heart with the point of exit of the nerve from the 

 neural tube. The nerve fibres in no way influence the growth or 

 the arrangement of the mesenchyme cells with which they are 

 associated. The fibres assume the same course about these cells 

 as they do in non-cellular clots (fig. 6). 



The relation, however, of the cellular outgrowths to the nerve 

 fibres was different in the single case in which the neural tube 

 together with its adjoining myotomes were transplanted to the 



