18 



PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



this mode of cell reproduction. The latter example furnishes many 

 instances in which a number of cells with entirely different attributes 

 from the parent cell develop in the interior of a cell, such as the develop- 



Fig. 6.— Karyokinesis. {Kh-in.) 



A. ordinary nucleus of a columnar epithelial cell ; B, C, the same nucleus in tile stage of convolution : 

 D, the wreath, or rosette form : E, the aster, or single star; F, a nuclear spindle from the Descemet's 

 endothelium of the frog's cornea ; G, II, I, the diaster : K, two daughter nuclei. 



ment of pus-corpuscles in the interior of different tissue-cells in inflam- 

 mation (Fig. T). 



The best object for the study of cell reproduction by division, and 



the one of most interest for us, is 

 found in the fertilized ovum of 

 mammals. 



As the ovum approaches maturity, 

 even before impregnation takes place, 

 the germinal vesicle becomes obscure 

 and more and more irregular in out- 

 line, its membrane and reticulum 

 disappear, and the germinal spot is 

 broken up. What remains of the 

 germinal vesicle becomes converted 

 into a striated, spindle-shaped body, 

 which moves to the surface of the 

 ovum, to there undergo division into 

 two parts. One part becomes ex- 

 truded from the ovum to form what 

 is known to embryologists as the polar cell, and is soon followed by a 

 second similar cell, while the portion of the spindle remaining within 

 the ovum forms a new nucleus, the female pronucleus, from which, in 

 conjunction with the male elements, the future embryo is developed. 



Fia. 7.— The Formation of Pus-Cor- 

 puscles in the Interior of Epithe- 

 lial Cells, showing Endogenous 

 Cell-Formation. (Rankc) 

 A, single cylindrical cell from the human bile-duct ; 

 B, a similar cell containing two, C containing four, and 

 D numerous pus-cells ; E, isolated pus-corpuscles ; 

 F, a ciliated epithelial cell from the human respiratory 

 tract, containing a single pus-corpuscle : and G, a pave- 

 ment epithelial cell from the urinary bladder of man, 

 containing numerous pus-corpuscles. 



