2l8 ON THE IDENTITY OF STRUCTURE OF PLANTS AND ANIMALS 



Animal with 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 

 subsequentl)' 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 expressed : 

 — In all the animal tissues the so-called nucleus (Endoplast) is the 

 homologue of the primordial utricle {with nucleus and contents) (Endo- 

 plast) 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 absolute 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. 



Thus in the Plant, the Endoplast of the young tissue becomes 

 a "primordial utricle," in which a central mass, the "nucleus," may or 

 ma}' 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 tissue. 



The periplastic substance follows to some extent the changes of 

 the endoplast, inasmuch as it general!)-, 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 under- 

 goes its own peculiar metamorphoses quite independently of the 

 endoplast. — This the Lecturer illustrated by the striking case of the 

 Sphagnum leaf, in which the peculiarly thickened cells can be shown 

 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 disappearance of the primordial utricle in woody cells 

 in general, — in confirmation of the same views. 



Now, these metamorphoses of the periplastic substance are two- 

 fold : I, Chemical ; 2, Morphological. 



