ANIMAL CELLS. 



33 



fore, we have a structure which entirely corresponds 

 with a vegetable cell. 



It has, however, been customary with authors, when 

 describing cartilage, to call the whole of the structure 

 of which I have just given you a sketch (fig. 2, a d) 

 a cartilage-corpuscle, and in consequence of this having 

 been viewed as analogous to the cells in other parts of 

 animals, difficulties have arisen Flo 2 



by which the knowledge of the 

 true state of the case has been 

 exceedingly obscured. A carti- 

 lage-corpuscle, namely, is not, as 

 a whole, a cell, but the external (P%<* 



layer, the capsule, is the product 



of a later development (secretion, excretion). In young 

 cartilage it is very thin, whilst the cell also is generally 

 smaller. If we trace the development still farther back, 

 we find in cartilage, also, nothing but simple cells, iden- 

 tical in structure with those which are seen in other 

 animal tissues, and not yet possessing that external 

 secreted layer. 



You see from this, gentlemen, that the comparison 

 between animal and vegetable cells, which we certainly 

 cannot avoid making, is in general inadmissible, because- 

 in most animal tissues no formed elements are found 

 which can be considered as the full equivalents of vege- 

 table cells in the old signification of the word ; and be- 

 cause in particular, the cellulose membrane of vegetable 

 cells does not correspond to the membrane of animal 

 ones, and between this, as containing nitrogen, and the 

 former, as destitute of it, no typical distinction is pre- 

 sented. On the contrary, in both cases we meet with a 



Fig. 2. Cartilage-cells as they occur at the margin of ossification in growing 

 cartilage, quite analogous to vegetable cells (cf. the explanation to fig. 1). a c. In. 

 * more advanced stage of development, d. Younger form. 



3 





