Identity of Structure of Plants and Animals. 237 



Thus in the plant, the endoplast of the young tissue be- 

 comes a " primordial utricle," in which a central mass, the 

 " nucleus," mayor may not arise ; persisting for a longer or 

 for a shorter time, it may grow, divide and subdivide, but it 

 never (?) becomes metamorphosed into any kind of fcissue. 



The periplastic substance follows to some extent the 

 changes of the endoplast, inasmuch as it generally, though 

 not always, grows in when the latter has divided, so as to 

 separate the two newly-formed portions from one another ; 

 but it must be carefully borne in mind, though it is a point 

 which has been greatly overlooked, that it undergoes its own 

 peculiar metamorphoses quite independently of the endo- 

 plast. This the lecturer illustrated by the striking case of 

 the sphagnum leaf, in which the peculiarly thickened cells 

 can be shewn to acquire their thickening fibre after the total 

 disappearance of the primordial utricle ; and he further 

 quoted M. von Mohl's observations as to the early disappear- 

 ance of the primordial utricle in woody cells in general, in 

 confirmation of the same views. 



Now, these metamorphorses of the periplastic substance 

 are twofold : 1. Chemical ; 2. Morphological. 



The chemical changes may consist in the conversion of the 

 cellulose into xylogen, &c. &c, or in the deposit of salts, silica, 

 &c, in the periplastic substance. Again the periplastic sub- 

 stance around each endoplast may remain of one chemical 

 composition, or it may be different in the outer part (so-called 

 intercellular substance) from what it is in the inner (so- 

 called cell-wall). 



As to morphological changes in the periplastic substance, 

 they consist either in the development of cavities in its sub- 

 stance — vacuolation (development of so-called intercellular 

 passages), or in fibrillation (spiral fibres, &c.) 



It is precisely the same in the animal. 



The endoplast may here become differentiated into a nu- 

 cleus and a primordial utricle (as sometimes in cartilage), 

 or more usually it does not, — one or two small solid particles 

 merely arising or existing from the first, as the so-called 

 " nucleoli ;'' — it persists for a longer or shorter time ; it 

 divides and subdivides, but it never (except perhaps in the 



