166 J. M. D. OLMSTED * 
obliterated and all the new material goes to form the head 
(figs. 6, 7). Without exception, the first eye to make its ap- 
pearance is the one which les nearer the anterior boundary of 
the uncut surface (figs. 6c, 7c). This is likewise the rule in the 
regeneration of heads along oblique cuts (Rand and Boyden, ’13). 
The other eye develops later and remains smaller for many days, 
or even until the worm disintegrates (figs. 5g, 6e, 7e, 8, 9). 
8 
Fig.8 The most nearly symmetrical of all pieces obtained. Piece taken 
from left side of worm near pharynx. Drawn in fixing fluid on 13th day after 
operation. Brain and nerve cord (cross hatched) filled in from serial sections. . 
Fig. 9 Case similar to that of figure 8, 15 days after operation. New pharynx, 
and unequally developed eyes. 
tt b 
Fig. 10a A camera drawing of a frontal section whose photomicrograph is 
given in figure 11, showing position of nervous system. 106. Whole animal 
reconstructed from serial sections and from last drawing of piece while alive. 
New tissue at the left of broken line. 
One of the striking characteristics of these triangular pieces 
is the condition of the nervous system. Frontal sections of six 
such pieces, after regeneration of one or both eyes, showed that 
the two new nerve cords are joined to the ends (anterior and 
posterior) of the remnant of the old nerve cord (figs. 8 to 11). 
