CELLS. 23 



less, as it is not to be doubted that, together with the latter 

 process, a multiplication of nuclei by division takes place, in 

 which an elongated parent nucleus, with two nucleoli, breaks 

 up into two by the formation of a constriction which gradually 

 deepens in the middle. 



The further destiny of the parent cells, with a partition and 

 two nuclei, is not always the same. As a rule, it appears 

 that in each, two perfect secondary cells afterwards become 

 evident, which may serve as a demonstration that the partition 

 is double from the very first. At other times, distinct secondary 

 cells are not recognisable, which however does not imply that 

 there exists a mode of cell-development by the mere formation 

 of partitions, but only that in such cases the secondary 

 cells do not become distinctly separated from the parent cells. 

 Whether the one process or the other take place, it rarely 

 stops at one performance, but is generally repeated a certain, 

 often very considerable number of times ; in fact, as long as 

 the organism grows. The parent cells either remain, or they 

 cease earlier or later to be histologically distinct structures, 

 and coalesce with the substance which unites the cells as a 

 matrix. The occurrence of this endogenous cell-development, 

 which may be called cell-development around the collective 

 contents, and which agrees in all essential points with free cell- 

 development around investing masses, has been made out with 

 certainty in the young cartilage of all animals, and probably 

 occurs in embryonic organs in general, in which, from the 

 moment when they consist of actual cells, the total growth 

 essentially depends upon a self-multiplication of the cells 

 without free cell- development. Since, however, it is as 

 yet undecided, whether perhaps cell-development by division, 

 to which attention has been very lately drawn, does not 

 play a part in the one case or in the other, our judgment, 

 so far as regards the latter, must as yet be suspended, until 

 more particular investigations have been undertaken; and 

 the same holds good for many organs of the adult, as the 

 horny tissues and certain glandular secretions. Only, when 

 secondary cells arc observed in parent cells, as especially in 

 the pituitary body and in the supra-renal capsules, there can 

 of course be no doubt as to the existence of endogenous cell- 

 development. 



