468 RICHARD ASSHETON. 
in the centre of which the mouth occurs subsequently. The 
direction of the flow here is, as in the case of the dorsal current, 
from before backwards (vide fig. 3). 
I have tried most carefully to find any indication of a ciliated 
ectoderm upon that portion of the neural plate which is folded 
up and becomes the neural tube. I can find no indication of a 
ciliation. 
The cavities of the brain and spinal cord of the adult are said 
to be lined by a ciliated epithelium. Although doubted by 
some authors, this has been satisfactorily demonstrated by 
others (vide Wightman, ‘ Studies of the Johns Hopkins Uni- 
versity,’ vol. iv). At what stage the cells that bound these 
cavities became ciliated I cannot say, but of every specimen 
which I have examined I can say that at the time of closure of 
the neural folds there is no motion of suspended particles at 
any spot along the neural groove, although a rapid current is 
produced along the external portion of the edges of the neural 
plate. 
Klein (6) has described a ciliation of the neural groove 
while still open in the chick, in embryos with about seventeen 
protovertebre. 
By the time that the neural folds have closed, except at 
quite the posterior end, the whole of the dorsal surface is 
ciliated, including the groove formed by the junction of the 
neural folds. By far the most rapid movement of particles 
takes place along the line indicated by the large arrows in 
fig. 4 (N.B.C.), which is along the extreme outer limit of the 
neural plate, or rather over that portion of the epiblast which 
subsequently gives rise to the sensory ganglia of the 5, 7, 8, 
9, 10 cranial and the spinal nerves. 
The ciliation now spreads very rapidly, and by the time the 
embryo with seven or eight mesoblastic somites measures about 
3 mm. in length, which is about the time of the perforation of 
the anus, the whole surface of the embryo is ciliated, but the 
currents vary very much in intensity. 
Fig. 5 is a diagram of the currents produced by the cilia as 
seen from the side. 
