54 



THE TISSUES OF PLANTS 



ginated, appears but as a small opaque body, which is either 

 centrally located, or attached to one of its walls. 



Thus, according to Schleiden, the cytoblast or nucleus 

 visible in the cellule, has originated the cellule itself. It 

 is seldom, however, that the cytoblast remains visible for 

 any length of time after the cell has been fully formed; 

 generally, it is re-absorbed. 



The cytoblast is beautifully apparent in the moniliform 

 hairs of Tradescantia. Virginica, 



The elementary cells which compose the tissues of ani- 

 mals also contain these nuclei or cytoblasts. 



Fig. 12. 



Nucleated cartilage cells from the Chorda dorsalis of a Lamprey. 



Of this we have a very beautiful and striking' proof 

 afforded in the above engraving. The Chorda dorsalis is 

 an extremely thin and delicate tube, composed of cells in 

 close opposition with each other, and enclosing the spinal 

 chord. It is, in fact, the vertebral column arrested in the 

 first stage of its development. This is its permanent con- 

 dition in the lamprey, and also in the lowest group of car- 

 tilaginous fishes. 



