CELL. 



[ 116 ] 



CELL. 



Fig. 113. 



Magnified 350 diameters. 



Cartilage cells from a fibrous velvety articular cartilage 

 of the condyle of a human femur ; all lying in a fibrous 

 basis, and easily isolated, a, single cells, with or without 

 thickening of the cell-wall, and one or two nuclei ; b, se- 

 condary cells, or cells of the first generation with one or 

 two nuclei, — one, two, five and many cells in the parent- 

 cells b' ; c, cells of the second generation, one to three in 

 those of the first, b,b; d, free group of secondary ceUs. 



ary cells are formed in the usual way in a 

 cell, almost or entirely filling it, and from 

 these other generations, either free, or all or 

 individual ones enclosed in parent-cells of 

 the second and subsequent generations ; or 

 only one secondary cell is formed in a cell, 

 whence cell-formation then proceeds in either 

 manner (fig. 113) ; or the secondary cell is 

 formed in a bud-like protrusion of the parent- 

 cell (see EcHiNococcus). 



The formation of a larger number of 

 nuclei within cells may be well arranged 

 under endogenous cell-growth, which fre- 

 quently precedes cell-formation, but may 

 also exist alone. Even in ordinarv endoo;e- 

 nous cell-formation (and also in segmenta- 

 tion) we not unfrequently find three and 

 four nuclei in one parent-cell, so that then, . 

 instead of two, a larger number of secondary 



cells are formed at once, as e. g. in 

 the liver-cells of embryos. In certain 

 animals {Cucullanus, Ascaris dentata, 

 Dlstoma and the Cestoidea), instead 

 of segmentation-globules in the first 

 stage of development, nuclei only are 

 formed in the ovum- cell, which do 

 not become surrounded by cell-mem- 

 branes until they have accumulated 

 in^o a large heap by successive endo- 

 genous growth. The same appears 

 to take place in the cells of the germ 

 of the Crustacea, in which from ten 

 to twenty nuclei frequently exist. The 

 numerous nuclei, however, in the 

 seminal cells of most animals appear 

 usually to have no connexion with 

 cell-formation, because the seminal 

 filaments are developed within them, 

 and the same applies to those cells of 

 the lower animals, the numerous 

 nuclei of which are converted into 

 urticating organs. Whether in these 

 cases the nuclei multiply by division 

 or endogenous growth is unknown. 



Cell-formation by division has been 

 observed in the coloured blood-cor- 

 puscles of the embryos of Birds and 

 Mammalia, and the earliest colourless 

 blood-corpuscles of the larvse of frogs 

 (tad])oles) ; it also probably occurs in 

 the colourless blood-corpuscles of 

 embryos and the chyle-corpuscles of adult 

 Mammals. In all these cases, the cells first 

 become elongated, and the single nuclei 



Fig. 114. 



Magnified 350 diameters. 

 Ivory cells from the tooth of a dog. 



