250 
Dr. Johnson's observations 
liest opportunity of putting them in practice, but with evi- 
dent mistrust as to the result (not however in the slightest 
degree doubting the accuracy of the above report), conceiving 
that no circumstance of this nature had yet occurred, in the 
many and repeated experiments I had performed upon these 
animals 'during the past and the preceding summer. 
Having a considerable number of the P. cornutce in my 
possession, I took at least one hundred of the most active, 
and made an incision on the side of the body in each, but 
only succeeded in one solitary instance in obtaining the wished 
for result. 
Looking over these planarize after the lapse of nearly a 
fortnight, I discovered that the incisions had, in by far the 
greater number healed, so that no evident difference existed 
between them and perfect un mutilated planariag. Preterna- 
tural excrescenses had taken place in several, and others had 
separated at the place of incision so as to become two animals, 
but only one planaria^ as before noticed, exhibited the very 
singular and astonishing circumstance of a double head. The 
additional head was in about six weeks equally perfect 
and well formed with the other, although it had not yet ac- 
quired the usual deep colour. In fig. i. is a delineation of 
this double headed planaria, such as it appeared under the mi- 
croscope when at rest; fig. 2 . as seen when in motion. In 
about two months after it had acquired this additional head, 
a fragment separated from the tail (the most usual place of 
separation) and was in progress towards its entire reproduc- 
tion, when it was accidentally lost — a second, and ultimately 
a third fragment was spontaneously separated from the same 
