60 THE CELL DOCTRINE. 



with the cavities which previously existed in it, is of 

 no more value in proving the independence of these 

 vesicles, than the fact that a rhombohedron of spar, 

 broken up with the hammer, into minute rhombohe- 

 drons, is evidence that those minuter ones were once 

 independent, and formed the larger bj their coales- 

 cence. 



Second, Schwann's view of the anatomy of the cell 

 was incorrect, since he regarded the nucleus as in- 

 variably present, whereas in certain vegetable cells 

 (as in Hydrodictyon, Vaucheria, Caulerpa, Sphag- 

 num), it is indubitably absent ; and since he did not 

 include the nitrogenous primordial utricle, discov- 

 ered by Mohl, in 1844,* as one of the elements of 

 the cell. 



Finally, Schwann's mode of cell-development is 

 erronous, having " been long since set aside by the 

 common consent of all observers ; " cell-development 

 always occurring by division, except in the embryo 

 sac of the Phanerogamia, the sporangia of Lichens, 

 and of some Algse and Fungi ; and even the free 

 cell-development of the latter is quite difterent from 

 that of Schleiden and Schwann, being by the develop- 

 ment of a cellulose membrane (periplast) around a 

 mass of nitrogenous substance (endoplast), which 

 may or may net contain a nucleus. 



The difference between the views of Schwann and 

 Huxley are best expressed by the latter in the con- 

 trast he draws between those of Schwann and Wolff: 



* The existence of the primordiul utricle is denied by many 

 botanists of the present day. 



