C 247 3 
XL Further observations on Planarice. By J. R. Johnson, 
M. D. F. R. S. 
Read March lo, 1825. 
About three years since I presented to the notice of the 
Royal Society a few observations on the genus planaria. 
From that period to the present having had no opportunity 
of extending my researches to more than two or three species 
in addition to those formerly described, I was unwilling to 
trespass upon the time of the Society by any further remarks, 
until I had ascertained the remaining species of this genus. 
A circumstance, however, attending some experiments in 
which I have been lately engaged, of rather a strange cha- 
racter, forming another interesting feature in the history of 
these very extraordinary animals, induces me to lay before 
the Society the present communication. 
The circumstance to which I allude, is that of the P. cornuta 
obtaining a second or additional head by an artificial incision, 
thus constituting a double headed planaria. 
At the period of my transmitting my former paper to the 
Society, I was not aware that any English author had written 
upon the same subject ; but was afterwards much surprised 
on learning that a Gentleman of Edinburgh, Mr. Dalyell, 
had published an account of these animals in 1814, in a work, 
having for its title “ Observations on some interesting Phoe- 
nomena in Animal Physiology, exhibited by several species 
of planaria.’' Failing to procure this work at the booksellers. 
