The Microscope. 69 



•complete metamorphosis whilst passing through their evolutions. 



Turpin also says that; a "tree, like every other organized being, 

 begins its existence in the form of a single globule, or mother- 

 vesicle." From this we are led to conclude that even before 

 1830 the cellular theory had already been formulated and estab- 

 lished, at least with reference to plants. 



During all this time zoologists had not kept pace with the 

 botanists. It is true, however, that now and then the analogy 

 between the two kingdoms of Nature had been pointed out, and 

 €ven striking resemblances had been observed ; but in reality, 

 Dutrochet in 1824, was the first to promote the idea that animals 

 and vegetables are organized on the same plan ; that both de- 

 velop in the same way, and finally that in animals also all tis- 

 ^sues are composed of cells. He says : " It is evident that all 

 •organic tissues of vegetables are derived from the cell, and obser- 

 vation now proves the fact that the same holds good for animals. 

 . . . All the tissues, all organs of animals, are really nothing 

 else but cellular tissue variously modified." 



Although Dutrochet has not been succesful in proving his 

 thesis (his descriptions, at least with regard to animals, are of- 

 ten inexact and erroneous), it remains nevertheless true that he 

 was the first author to apply the cellular theory to animals. 



To Schwann, a disciple of Schleiden, belongs the honor of fur- 

 nishing the proofs and demonstrations for the thesis of Dutrochet; 

 and this he has done in a most brilliant manner in a memoir 

 which marks an epoch in the annals of Cellular Biology. In 

 this memoir Schwann takes up one tissue after another, and bas- 

 ing his arguments on a great number of most rigorous and most 

 accurate observations, he establishes forever the fundamental 

 doctrines of the " Cellular Theory," which may be summed up 

 in the following statements : 1st. All animals and plants are 

 ■exclusively formed of cells. 2d. All these cells are derived one 

 from another, beginning with the embryonic cells. 3d. Owing to 

 their natural evolution, these cells undergo more or less marked 

 modification before they arrive at that state which they present in 

 the adult tissues. 



We find a good summary of the researches of Schwann in 

 Valentin's " Repertorium," (1839), where we also find the name 

 ^' Cellular Theory." 



John Goodsir in 1845, and later on also Virchow, applied this 



