PLANARIA. nalt 
About the middle of September, I selected five prolific Planarix, 
which were isolated in watch-glasses. An ovum was visible in each. In 
three days three were free of the ovum, and after three days, I observed 
two ova in each of the two watch-glasses. But it appears that in general 
the ovum is deposited within twenty-four hours of the time the Planaria 
is isolated. When produced, such ova are of a reddish-orange colour, 
fig. 12. 
During the progress of such experiments, the Planarize had multi- 
plied greatly in the vessel, and many white, minute, animalcular subjects, 
about half a line long, which I conjectured to be the young, were crawl- 
ing on its sides. 
The adults lurk below among mud. This animal is rare. 
Piate XV. 
Fic. 7. Planaria fodine—Quarry Planaria. 
8. The same, enlarged. 
9. Head, shewing the eyes, enlarged. 
10. Prolific specimen (with an ovum), slightly enlarged. 
11. The same, more enlarged. 
12. Ova. 
d.—PLANARIA ARETHUSA—The Fountain Planaria.—Plate XVI. Figs. 10, 
Tee Wot a los TOR Wi. 1S obo: 
Nothing is more perplexing to the naturalist than shght and inde- 
finite distinctions, and the natural and accidental changes incident to the 
lower animals. He may be thence led to constitute new species from 
simple varieties, or to admit as permanent what is only transient. It 
is scarcely possible to guard against such errors, which are of perpetual 
occurrence. 
The Planaria arethusa occupied my attention a number of years ago, 
when some general points distinguishing its nature were established. 
But the diversities occurring among a number of specimens dwelling ¢ 
seventy miles apart from the subjects previously under investigation, 
suggested that the latter might be a new species. It will not be void of 
