338 FLEXNER. [VoL. XIV. 
indicate the ease and variety of the development in these forms 
of duplicate parts. A knowledge of the histology of the re- 
generative phenomena in the nervous system is of interest, 
therefore, not alone in itself for its bearing on the question of 
the growth of highly specialized organs, but as affording a 
basis for a closer study of the phenomena of heteromorphosis 
in these animals. 
The methods employed in this study consisted in (A) de- 
capitation of the worms ; (4) decapitation to which was added 
an incision in the longitudinal axis, passing through the entire 
thickness of the animal, and extending about one third of its 
length; (C) complete longitudinal division with and without 
decapitation. At different periods in the process of regenera- 
tion the worms were killed with HgCl,, formalin 5%, alcohol 
or osmic acid (Flemming’s and Hermann’s solutions), hardened 
and sectioned in paraffin. A number of staining agents were 
employed. 
The decapitation was performed on the extended animals, 
the precaution having been taken to remove the entire cephalic 
extremity and contained nervous ganglia. 
When partial longitudinal incision was also carried out, the 
object of which procedure was to produce double-headed forms, 
it was found necessary, in order to prevent healing, to separate 
the incised halves every twelve hours or oftener for the first 
two or three days. 
After complete longitudinal division, each half immediately 
becomes rolled up in the form of a spiral, which gradually 
unwinds as regeneration proceeds. 
The rapidity of the regeneration of new and duplicate parts 
varies in several ways. The shortest periods were noted where 
a single extremity was replaced (head or tail); a longer period 
is required for the completion of two parts of the same sort 
(double heads); and the longest are observed in the regenera- 
tion of the longitudinally divided halves. 
Temperature also plays an important part. At the quite 
uniform and moderately low temperature of Woods Holl, the 
growth takes place far less rapidly than at the much more 
elevated temperatures which prevail in Baltimore during the 
