O12 JULIA B. PLATT. 
In the anterior segments of the trunk the cells of the neural 
Anlage form two layers at its ventral edge before coming in 
contact with the mesenchyme below. As the Anlage, in this 
early stage, lies between the sharply bounded spinal cord on 
the one hand, and no less distinct myotome on the other, it is 
easy to determine the number of cells composing it by counting 
the nuclei on successive sections. The result shows that there 
is no early accumulation of cells in definite regions pointing to 
the formation of ganglia, and consequently no primitive seg- 
mentation. Comparing segment with segment, one finds a 
gradual diminution of the Anlage as one approaches the tail. 
My purpose in counting the cells was chiefly to determine the 
number of neural cells taking part in the formation of the 
connective tissue in the posterior portion of the vagus segment 
which contains no spinal ganglion, and in the following seg- 
ment where the ganglion, which develops at a relatively late 
stage, consists merely of a small group of cells at the root of the 
motor nerve. 
Counting the neural cells between the spinal cord and the 
first myotome, before the neural Anlage meets the mesenchyme, 
I find on the left side of the embryo 166 cells. The order on 
successive sections is—10, 8, 8, 7,5, 5, 5, 7, 4, 6, 9, 6, 4, 4, 5, 
6, 4, 5, 5, 9, 6, 4, 5,4, 6, 4, 5, 4, 6. In the following segment 
there were 126 cells, scattered quite as irregularly. In the 
third segment 123, and in the fourth 125. The slight increase 
in the number of cells in the fourth segment is probably due 
to preparation for the large brachial ganglion that lies in this 
segment. ‘The following segments show rapid reduction in the 
number of neural cells. 
I then counted all of the connective-tissue cells above the 
level of the motor nerve-root in the first trunk segments of 
the series from which figs. 13, 14,15, 16 are taken, where 
the neural crest of the anterior segments has united with the 
mesenchyme, and forms a loose tissue of two layers at each 
side of the spinal cord. 
The result gives for the posterior part of the vagus segment 
on the left side of the embryo 150 cells. Their order in section 
