Magnified 350 diameters. 



Cartilage-cells from a fibrous velvety articular car- 

 tilage 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, secondary cells, or cells of the first genera- 

 tion, with one or two nuclei one, two, five, and many 

 cells in the parent-cells 6'; c, cells of the second gene- 

 ration, one to three in those of the first, bb; d, free 

 group of secondary cells. 



mentation) we not unfrequently find three 

 and four nuclei in one parent-cell, so that 

 then, instead of two, a larger number of se- 

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

 the liver-cells of embryos. In certain ani- 

 mals ( Cucullanus, Ascaris dentata, Distoma, 

 and the Cestoidea), instead of segmenta- 

 tion-globules, in the first stage of develop- 

 ment, nuclei only are formed in the ovum- 

 cell, which do not become surrounded by 

 cell-membranes until they have accumu- 

 lated into a large heap by successive endo- 

 genous growth. The same appears to take 

 place in the cells of the germ of the Crus- 

 tacea, in which from ten to twenty nuclei 

 frequently exist. The numerous nuclei, 

 however,* in the seminal cells of most ani- 

 mals appear usually to have DO connexion 



CELL. 

 Fig. 110. 



Magnified 350 diameters. 

 Ivory-cells from the tooth of a dog. 



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 ob- 

 served in the coloured blood-corpuscles of 

 the embryos of Birds and Mammalia, and 

 the earliest colourless blood-corpuscles of 

 the larvae of frogs (tadpoles) j it also pro- 

 bably occurs in the colourless blood-cor- 

 puscles of embiyos and the chyle-cor- 

 puscles of adult Mammals. In all these 

 cases the cells first become elongated, and 

 the single nuclei appear to become divided 

 into two ; the cells are then constricted in 

 the middle and finally resolved into two, 

 each with a nucleus (PI. 49. fig. 36). 



A peculiar kind of cell-growth, most 

 nearly allied to division, occurs in the cells 

 of the ivory of the teeth ; in which the nu- 

 clei, while continually elongating, enlarge 

 from time to time and become constricted, 

 so that whilst that portion next the ivory 

 ossifies, the remainder serves to a certain 

 extent as a reserve for the subsequent for- 

 mation of newly ossifying portions (fig. 110). 

 The term cell is frequently used in a 

 totally different sense, to denote a partially 

 closed space, or the cup-like body enclosing 



