CELLS. 



27 



cell membranes. Something similar appears to take place in 

 the cells of the germ in the Crustacea, in which 10 — 20 

 nuclei are often found (Rathke, 'De Anim. Crustac. gen./ 

 Regim. 1841). On the other hand, the numerous nuclei in 

 the spermatic cells of most animals are, in general, in no w ay 

 connected with cell- deve- 

 lopment, since the spermatic 

 filaments are developed in 

 them ; and the like holds 

 good of those cells of the 

 lower animals, whose multi- 

 tudinous nuclei are changed 

 into thread-cells. The im- 

 port of the number of nuclei 



in certain nerve-cells, and in 



a 



the large cells of the bone- 

 medulla, which Robin and I 

 have observed, is doubtful ; 



in the latter, I think it is not improbable that the multiplication 

 of thenuclei is preliminary to theirbreaking up into smaller cells. 

 In all these cases, it may be easily demonstrated that the nuclei 

 multiply spontaneously, but it is generally doubtful whether 

 this happens by division or by endogenous development. 



[Cell- development round a mass of blastema containing a 

 nucleus in its interior, which may take place either freely or in 

 an endogenous manner (cell-development round portions of 

 contents), had long ago been seen by von Siebold in the ova of 

 Distoma globiporum, and by Bergmann in the cleavage-masses 

 of Rana, but no further importance was attached to it. Vogt 

 and Nageli were the first who regarded this cell-development, 

 as a deviation from the theory of Schleiden and Schwann, 

 whereupon, supported by observations upon embryos, I (in 1844, 

 ' Entwick. d. Cephalopoden') placed this as a second kind of cell- 

 development, under the name of " cell-development round in- 

 vesting masses," beside that which takes place immediately 

 round nuclei, and pointed out its very extensive occurrence, 

 especially in embryos, where at first it is the sole mode. Later 



Fig. 7. a. Peculiar granulated cells with many nuclei, from the youngest medullary 

 cavities of the flat hones of the skull in man, x 350. 



