^36 Thomas H. Huxley, Esq., on the 



existence in the former of a local physico-chemical differ- 

 entiation ; while the latter are physically and chemically 

 homogeneous throughout. 



These facts, in their general outlines, have been well known 

 since the promulgation, in 1838, of the celebrated cell-theory 

 of Schwann. Admitting to the fullest extent the service 

 which this theory had done in anatomy and physiology, the 

 lecturer endeavoured to shew that it was nevertheless in- 

 fected by a fundamental error, which had introduced con- 

 fusion into all later attempts to compare the vegetable with 

 the animal tissues. This error arose from the circumstance 

 that when Schwann wrote, the primordial utricle in the vege- 

 table cell was unknown. Schwann, therefore, who started 

 in his comparison of animal and vegetable tissues from the 

 structure of cartilage, supposed that the corpuscle of the 

 cartilage cavity was homologous with the " nucleus" of the 

 vegetable cell, and that therefore all bodies in animal tissues, 

 homologous with the cartilage corpuscles, were " nuclei." 

 The latter conclusion is a necessary result of the premises, 

 and therefore the lecturer stated that he had carefully re- 

 examined the structure of cartilage, in order to determine 

 which of its elements corresponded with the primordial utricle 

 of the plant, — the important missing structure of which 

 Schwann had given no account — working subsequently from 

 cartilage to the different tissues with which it may be traced 

 into direct or indirect continuity, and thus ascertaining the 

 same point for them. 



The general result of these investigations may be thus ex- 

 pressed : — In all the animal tissues the so-called nucleus 

 (endoplasts) is the homologue of the primordial utricle {with 

 nucleus and contents) (endoplast) of the plant, the other 

 histological elements being invariably modifications of the 

 periplastic substance. 



Upon this view we find that all the discrepancies which 

 had appeared to exist between the animal and vegetable 

 structures disappear, and it becomes easy to trace the ab- 

 solute identity of plan in the two, — the differences between 

 them being produced merely by the nature and form of the 

 deposits in, or modifications of, the periplastic substance. 



