THE CELL DOCTRINE. 33 



A formidable obstacle for some time in the vtaj of 

 a law of development, applicable to animal' and vege- 

 table tissues, was the opinion, long entertained, that 

 the growth of animals, whose tissues are furnished 

 with vessels, is essentially difterent from that of plants ; 

 an independent vitality being ascribed to the elemen- 

 tary particles of vegetables growing without vessels. 

 So firmly was this believed, that the ovum, which 

 exhibited undoubted evidences of an actual vitality 

 at one period of its growth, was said by all phj'siolo- 

 gists to have had a plant-like growth. This obstacle 

 was removed in 1837, by Henle,* who showed that 

 an actual growth of the elementary parts of epithe- 

 lium took place without vessels. 



Taking up the nucleus as discovered by Robert 

 Brown, Schleiden,t in reference to its function, ap- 

 plies the name cytoblast {xuto<;, a cell, j^^darvq, a bud 

 or sprout), or " cell bud," and in a careful study of 

 its anatomy, discovers that " in very large and beau- 

 tifully developed cytoblasts, there is observed a 

 small, sharply defined body, which, judging from the 

 shadow which it casts, appears to represent a thick 

 ring, or thick-walled hollow globule."! One, two, three, 

 and even four of these may be present. Without fur- 

 ther present comment than that these characters, as 



* Henle, Symbolae ad Anatumiam vill.intest. Berol., 1837. 



t Schleiden, Beitrage ziir Phytogenesis, MuUer's Archiv, 1838, 

 p. ii ; Contributions to Phylogenesis, Sydenham Soc. Transl., p. 

 233. 



X The term nucleolus or nucleus-corpuscle (Kernkorperehen), 

 seems to have been first applied by Schwann. (See Introduction 

 to Schwann's Researches, Syd. Society's Translation.) 



