400 MONTGOMERY. [Vol. XIII. 



the second pair (six sections behind the first pair) ; both cells 

 of the third pair, just as those of the first, lie in the same fron- 

 tal plane. These three pairs lie in nearly the same horizontal 

 plane, and the distance separating the cells of the first pair is 

 about equal to that between the cells of the third pair ; but the 

 space between the cells of the second pair is greater, since they 

 are three sections apart. 



Behind the brain no neurochord cells are found in the lateral 

 nerve chords until the anterior region of the posterior intestine 

 is reached, being absent in the chords in the oesophageal region 

 of the body, as noticed by Burger ('90b) ; in C. lactezcs this is a 

 distance of several centimeters. 



Counting from before backwards, I find the first neurochord 

 cell of the chords just behind the oesophageal region on the 

 ventral side of the left chord; the second on the dorsal side of 

 the right chord; the third on the ventral side of the left chord; 

 the fourth on the dorsal side of the same chord; the fifth on the 

 ventral side of the same chord; the sixth and seventh on the 

 dorsal side of the right chord; the eighth on the dorsal side of 

 the left chord; the ninth and tenth on the same section, on the 

 dorsal sides of the right and left chords respectively. With 

 the exception of the last two, the cells enumerated are separated 

 (in the longitudinal axis) by considerable, though varying, 

 distances. The sequence of the first ten cells of the lateral 

 chords has been given as an example of their irregularity of 

 arrangement. It is unnecessary to reproduce here the dis- 

 tributive sequence of the approximately 159 cells whose posi- 

 tion I have determined, and it will be sufficient simply to state 

 the general results of this study of their arrangement. The 

 following table gives, for the four-fifths of the worm sectioned, 

 the numbers of these cells in both chords, and of each side of 

 each chord, all cells which are not typical neurochord cells 

 beina: excluded : 



