THE REGENERATION OF THE NERVOUS SYSTEM 
OF PLANARIA TORVA AND THE ANATOMY 
OF THE NERVOUS SYSTEM OF DOUBLE- 
HEADED FORMS. 
SIMON FLEXNER. 
DurRInG the summer of 1895, through the courtesy of Prof. 
C. O. Whitman, I enjoyed the pleasure of spending two 
months in the Marine Biological Station at Woods Holl. At 
the suggestion of Dr. Jacques Loeb, who extended to me the 
privileges of the Physiological Laboratory, I began the study 
which forms the subject of this paper. The following year I 
obtained additional material, which was sent to me at Balti- 
more, where the investigation was continued and brought to 
its present state of completion. My thanks are due to both 
these gentlemen for many acts of kindness, and to the latter for 
much valuable advice. 
The drawings which accompany this paper I owe to the 
kindness of Dr. Alice Hamilton. 
The researches of Loeb! upon heteromorphosis have shown 
that it is possible, through the use of several different pro- 
cedures, to bring about a substitution of an organ of one 
physiological value for that of another, and even to cause to be 
developed in one part organs which normally belong to widely 
removed localities. The light which the observations have 
thrown on the underlying forces and the manner of the 
formation of organs is considerable ; the study of the histologi- 
cal details of the process of organ-building in such cases has 
been little pursued. 
That heteromorphosis can be produced experimentally in the 
planarian has been proven by Van Duyne,? whose studies also 
1 Untersuchungen zur physiologischen Morphologie der Thiere, Wiirzburg, 
1891 and 1892. 
2 Ueber Heteromorphose bei Planarien, Archiv f. die ges. Physiologie, LXIV, 
1896, 569. 
