120 PLANARIA. 
s 
Its history in the Treatise on Planaria in 1814, Jeft numerous in- 
teresting questions unnoticed, therefore, in the hopes of verifying facts, and 
of correcting errors, a rigorous search was not only renewed in the very 
place where they were formerly not difficult to be taken, but extended 
over the neighbouring districts for several years, yet not a single speci- 
men could be discovered. 
A favourable opportunity at length conducted me to the original 
sites of these animals in the year 1822. My search was resumed, and 
it proved successful. I collected fifty with great facility on the 8th of 
May. 
However, some other animals, sufficiently numerous in the same 
place on former occasions, did not now appear, either having been extir- 
pated, or from still lurking in their retreats, as the weather was chill. 
There are conditions, yet mysterious to mankind, regulating the preser- 
vation and multiplication of animated beings. They cease to exist in 
particular places for a time without absolute extirpation from the district. 
Their numbers may be so reduced that they escape farther observation. 
All the preceding Planariz were of a beautiful grass-green ; they 
seemed nearly of equal size ; and almost the whole contained ova grouped 
in every possible arrangement. At least ten or twelve could be enume- 
rated in several ; sometimes in the right, sometimes in the left of the 
body : one or two were advanced a little before the rest. Their position 
was so much diversified, that it was never alike in any two specimens. 
From May 17, shining corpuscula, together with what seemed de- 
‘aying animal fragments, appeared in the vessels containing the captive 
animals. The former proved so many ova liberated on decomposition 
of the Planariz, numbers perishing daily from the great heat of the 
season, which suddenly changed. Such was the mortality, that not one 
Planaria remained in a week. 
These creatures are very prolific, forty ova lay in a vessel which had 
contained only three. 
About 100 ova were now transferred to a place deemed suitable for 
exclusion of the young. But none came forth. 
Greater inequality, than previously, prevailed among a second colony 
