255 
on planarice. 
speaking, capsule, producing from 2 to 6 young. The period 
at which the young are excluded varies with the prevailing 
temperature ; the shortest period as seen by the following 
tables being 20, the longest 53 days, making a difference in 
this respect alone of more than a month. 
ISO. or Ova or 
Capsules. 
When deposited. 
No. of young. 
When evolved. 
No. of days. 
5 
Aug. 5 
16 
Sept. 25 
51 
1 
7 
5 
29 
53 
4 
14 
9 
30 
47 
5 
18 
31 
10 
23 
12 
Sept. 2 
48 
22 
20 
27 capsules containing 109 young, being an average of 
four young to each capsule. 
The P. nigra, if artificially divided in two or more parts, 
will have the lost portion restored in about a fortnight or 
three weeks. One of these under a magnified form, with a 
renewed anterior extremity, is delineated at fig. 11, for the 
purpose of showing a circular range of black specks, or what 
are commonly called eyes, surrounding the outer margin of 
the head. This species does not, as far as I have been able to 
ascertain, separate like the P. cornuta by spontaneous divi- 
sion ; although, in common with the genus to which it be- 
longs, it is enabled to repair any mutilation to which it may 
have been exposed. 
J. R. JOHNSON, M. D. F. R: S. 
Bristol, Jan. ii, 1825. 
I 
