MORPHOLOGICAL STUDIES. 
185 
consequences of this conclusion are fatal to the observations 
which His recorded nearly ten years ago, and to which he has 
been true for nearly twenty years. 
The next stages in the formation of the spinal ganglia 
which we need consider are represented in Pis. XVIII, XIX, 
and XX, figs. 51, 55, 98, 99. 
The separation of the neural tube from the epiblast has now 
taken place, and the ganglionic Anlagen have also no longer 
any connection with the epiblast. The spinal cord has not yet 
really closed, for its lips have not met, and in all the figures 
they are sharply defined from the fused ganglionic Anlagen 
which lie between and above them. In all the figures, but 
especially in 55, 98, 99, the Zwischenstrang of His ( z .) is a 
prominent object. It is represented under very high power in 
figs. 98 and 99. As in Elasmobranchs, the ganglionic Anlagen 
now begin to grow down the sides of the cord, leaving their 
position above the lips of the neural tube ; a stage of this 
process, showing that they are still unconnected with the cord, 
is given in fig. 102. When the Anlagen leave the lips of the 
neural tube the latter close together, and all subsequent stages 
go on exactly as described in Elasmobranchs. As I can here 
record no new facts I leave the development of the spinal 
ganglia of the Chick at this stage. I have proved at least three 
things for the spinal ganglia of the Chick. (1) That they 
are direct epiblastic proliferations formed very early outside 
the limits of the spinal cord Anlagen ; (2) that there is no out- 
growth of cells from the spinal cord to form them ; (3) that the 
Zwischenstrang of His is that part of the epiblast which just 
fails to play any part in the formation of the ganglia. A 
fourth conclusion may be drawn, and this also holds for Elas- 
mobranchs and other forms. It is that there is no form element 
in the spinal ganglia corresponding to that portion of the 
cranial ganglia which is derived from the sensory epithelium 
of lateral sense organs. 
