162 HOWARD AYERS 
the higher forms would come into being. I think this transfor- 
mation has taken place in the evolution of the vertebrate stock. 
Regarding the termination of the fibers leaving the cord in the 
ventral root, it is plain that not all of them form end-plates on 
the muscle (fig. 5). Some of them form nerve nets which lie 
superficially upon the muscle plates and are apparently inter- 
muscular fibers. There are, however, gradations between a few 
anastomoses between adjacent fibers of a bundle and the extreme 
of complicated nerve net. In the former condition I have found 
anastomosing fikers to terminate in end-plates, but where an 
extensive net is formed I have not seen terminals leaving it to 
enlarge into end-plates. They may occur, nevertheless, as in a 
few instances fibers from the superficial net seemed to penetrate 
into the muscle plate (fig. 5, D). The figures of Kutchin and 
Dogiel drawn from methylen-blue and Golgi preparations do not 
show the actual structure of the end-plates. 
My observations of the neuromotor mechanism of Amphioxus 
indicate that, while both nerve and muscle structure is much 
less differentiated than in the higher forms, it is doubtless an 
ancestral stage. The addition of sheaths would convert the 
nerve fibers into the structures we find higher up. Bdellostoma, 
Ammocoetes and Petromyzon furnish some of the intermediate 
stages to this process of acquisition of protective coverings by 
the nerve fibers. The same is true as regards the relation of the 
dorsal and ventral roots. Amphioxus has them as separate and 
distinct bundles throughout their root territory, but they are 
found ending peripherally in the same territory (the myotomes), 
but on different business. Again, Bdellostoma, Ammocoetes, 
and Petromyzon present us with stages which show how the 
condition in the higher forms has been arrived at. 
The ventral root is relatively as extensive as in the higher 
forms, 1.e., it runs to the extreme limit of the muscle organ to 
which it is assigned and is a long branching nerve, not a brush 
of fibers. 
Winding Way and Valley Road, Cincinnati 
March 21, 1921 
