History of a transient nervous apparatus in certain Ichthyopsida. 381 



are "peripheral" because they do not form part of the axial series, 

 aüd it is convenient, owing to the manifold groupings under which 

 they appear, to treat of them apart from their "central" fellows. 

 Going back once more to sections of early embryos (6 — 8 mm), in 

 which the cells of the future spinal ganglia are beginning to migrate 

 from between the lips of the cord, it may be established, as indicated 

 a few pages previously, that in and among these cells there are some 

 which are already becoming ganglionic (Figs. 2 and 5 gl.c and gl.cc). 

 Whilst developing ganglionic characters, these cells are in course of 

 migration into the mesoderm ; but their goal is not that of the as 

 yet non-ganglionic cells of the future spinal ganglia , it lies in the 

 direction of the apex of the myotome, as evidenced by Figs. 10, 17 

 and others. So manifold are the appearances presented by these 

 wandering cells that it is difficult to give an account of them without 

 describing a great number of special cases. One frequent feature is 

 a tendency on the part of the wandering cell to spin nerve-processes 

 in the course of its migration. And, just as a spider, when moving 

 from one point to another, often spins a thread keeping it connected 

 with its starting-point, so these cells usually spin out processes 

 ending somewhere among the ganglion-cells of the top of the cord 

 (Fig. 15). 



At the other pole of the cells their processes are very often 

 directed over the tip of the myotome, and many of the cells in their 

 wanderings take the same course, coming to lie near the myotome 

 (Figs. 45, 75 and others) and even outside it just beneath the epi- 

 blast. In later stages they may be found as far down as the lateralis 

 nerve, though this is of somewhat rare occurrence. 



Their processes will be referred to again in treating of the nerves 

 of the system ; but it may be also briefly mentioned at this point that 

 these wandering ganglion-cells very frequently become applied to, or 

 even "mixed-up" with, transient nerves. Another favourite resting- 

 place appears to be the epithelium of the apex of the myotome. In 

 this latter position they are often encountered , sometimes forming 

 such regular members of the epithelium that one is tempted to a 

 belief in their origin in loco. 



It is, of course, difficult to prove this, more especially in view 

 of their wandering powers, but none the less figures like Figs. 85, 

 93 and 94 certainly afford some warrant for the opinion. 



In connection with these cells of the myotome-apices, it is worthy 



