PLANARIA. Ill 



About the middle of September, I selected five prolific Planariae, 

 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 Planarioe 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. 



PLATE XV. 



FIG. 7. Planaria fodince 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, 

 11, 12, 13, 14, 15, 1G, 17, 18, 19. 



Nothing is more perplexing to the naturalist than slight 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 aret/msa 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 



