on the planaria, 253 
The following is the result of this experiment during the 
first month. 
No. ofPlanariae. No. of Fragments. 
15 * placed together, threw off 16 
10 separately - 13 
25 produced _ - 29 
These 25 planarise, now placed together, detached in the 
course of the second month 33 additional fragments, making 
a total of 62. Supposing therefore this operation to con- 
tinue in full force eight months in the year, (and I find it 
unchecked even in the present month of January) we should 
have in the whole 248 fragments, an average of about 10 to 
each planaria ; but if we allow these creatures to multiply in 
a double or treble degree when at liberty, and supplied with 
proper food, we may then form a tolerable estimate of the 
extent to which their reproductive powers might be carried. 
In concluding this history of the P. cornuta, I may remark, 
that the smallest portion detached from the tail, so small in- 
de^ as to be scarcely perceptible, is sufficient to constitute the 
active principle or germ of the future animal ; but in this 
case these animals when perfect are so extremely small, as 
to lead one at the -first glance to believe that the parent ani- 
mals produced their young perfect and in a living state ; that 
they were in fact viviparous. 
I shall close this paper by a few general observations on 
the planaria nigra, the most common of the British planariae. 
