Development of the Infusoria. 253 



maxim " Omne vivum ex ovo," is for me, as well as Ehren- 

 berg, equally binding upon the infusorial tribes. I certajnly 

 think it very possible that there may be a generatio equivoca of 

 eggs, but not of perfect animals ; but our data are as yet quite 

 insufficient for the demonstration of the question. 



V. On the supposed Conneclmi between the Vegetable and Animal 

 Kinf^doms. 

 It is very commonly an admitted fact, that vegetables and 

 animals touch one another in their lower degrees — that they even 

 pass into each other, — that not only in one genus do we find 

 both animals and plants, therefore species from the two king- 

 doms of nature which can be separated by no generic distinc- 

 tion, but that even a plant often produces an animal which, du- 

 ring its growth, again changes into a plant. I must admit that 

 these notions were once very attractive to me ; that the globules 

 of the blood were simple monads, which were formed from the 

 living animal matter, like the infusoria from dead animal mat- 

 ter; that the Ectosperma produced monads which disappeared 

 after the short life of an hour, and grew up to Confervae. I 

 not merely believed this myself, but have publicly taught it as 

 an acknowledged fact, till I took the microscope in my hand and 

 experimented for myself. I have now perhaps fallen into the 

 other extreme ; for, certainly, I have never succeeded in obser- 

 ving the separation of the globules of the blood from the paren- 

 chyma, although I do not pretend to deny its possibility ; nor 

 have 1 at any time seen how animals change into plants ; and, 

 notwithstanding Spallanzani's often repeated experiments, doubt 

 very much of the resurrection of Furcularia after having been 

 dried up for more than a year. When Treviranus, Bory St 

 Vincent, and others, have seen globules issue from the tubes of 

 the Confervae and swim freely about like infusory animalcules ; 

 when Edwards has seen Confervae again spring from these 

 globules after settling ; when Unger and others have seen ac- 

 tive globules, which he calls Monads, issue from the Ectosper^ 

 ma clavata ; 1 do not doubt the fact of globules having issued 

 from these cryptogamic plants, which sprung about in different 

 directions : these motions seem voluntary, therefore they are ani- 

 mals ; they are very small and round, therefore they are mo- 



