138 JOHN BEARD. 
here, it also follows that the ganglia of the posterior roots are 
primitively ganglia of these branchial sense organs. Originally 
connected directly with its branchial sense organ, the ganglion 
of a posterior root has now left its primitive position and has 
come to lie in the mesoblast, being only connected with its 
sense organ by nerve-fibres. In this conclusion as to the 
nature of the ganglion I am again independently in agreement 
with Froriep and Spencer. 
In describing the schematic development of a dorsal root 
I have I think sufficiently emphasized its true nature. Primi- 
tively a dorsal root of a cranial nerve is the nerve of a gill- 
cleft, and is apparently only connected withthe innervation of its 
cleft. It sends fibres from the brain to the sense organ and 
ganglion above the cleft, thence other fibres pass to the 
musculature and walls of the cleft (fig. 50). 
It is not without importance to notice that any division of 
the dorsal root of a cranial nerve into so-called dorsal and 
ventral branches is primitively absent (fig. 50). Such divi- 
sions only occur in the later development in consequence of the 
separation of the ganglion from the skin, and of the formation 
of a greater number of branchial sense organs. Of course the 
ventral branch is there from the start, but in itself it is mainly 
motor and gives rise to no ganglion, and probably never has 
sense organs in connection with it. It certainly is not directly 
concerned in the innervation of a primitive branchial sense 
organ. Through a misunderstanding of this point Professor 
Froriep has been led into rather serious errors as to the nature 
of the dorsal roots. He concluded from Van Wijhe’s 
researches, and I must admit, not without reason, for the 
matter is there very vaguely stated, that the branchial sense 
organ and ganglion could occur on the ventral branch of a 
cranial nerve as well as on a dorsal. This conclusion led him 
to the opinion that the auditory nerve is a ventral branch. 
The blame of the matter lies very much at the door of 
Van Wijhe, for he described a cranial nerve (dorsal root) as 
typically possessing two branches, a dorsal and a ventral one, 
both of which could possess a ganglion. Now, we have seen in 
