/// the Aitiiiial hdKj'loiii. 369 



The epithelium of the urinary bhiJder ot diflereut luauiuKil.'*, 

 especially the mouse ami the dog, has recently received a 

 minute iiivesti<j:ation at the hands of A. 8. Uogiel, who writes 

 as follows*: — "In one and the same multilamellar epithf^- 

 liuni we Hud amitotic nuclear divi-^ion in theci.dlsof the up[)'U' 

 layers, and niit(jtic in those of the n'mainini^ layers." ''In 

 dilFerent mammals, but chieHy in the small Rodents, th(^ 

 U|)permost epithelial cells of the urinary bladder are of an 

 extraordinary size, and possess a lari>;e number of nuclei." 

 " We see that tlu^ process of multijilication of the nuclei in 

 the epithelial ceils of the uppermost layers is similar to that 

 which is found in the ;;'iant cells, leucocytes, epithelium of 

 the mammary glands, t?tc., namely direct amitotic nuclear 

 division, or even, more properly speaking', bud-formation." 

 The u|)perniost cells of the epithelium of the urinary bladder 

 liave a secretory function and give rise to the layer of mucus, 

 " which protects the mucous membrane of the bladder from 

 the effects of direct contact with the urine." If we furtlier 

 reflect that in multilamellar epithelia the ujj[)ermost layer of 

 cells always undergoes a gradual degeneration and is regene- 

 rated from the deeper layers, we see that in the case of 

 jiuiitotic nuclear division before us the biological conditions 

 are perfectly typical f. 



In cells which are ty])ical gland-cells amitotic division of 

 the nucleus is not rare \. Gland-cells in which an active 

 secretion fakes ^>/«ce alioa//s hace a considerable hulk and 

 itsuaVi/ a large nucleus ^^ tohich never divides by mitosis '^ 



* A. S. Dogiel, " Uobei- das I']pithol tier Ilarnblase,'' Archiv f. mikrosk. 

 Anatomie, 35 Bd., fSDO. 



t Amitotic miclear division in tlie epitlieliuin of the bladder has l)eea 

 found not only in Mammalsi, but also in I'rodela. Flemniing observed it 

 in the Salamander, but is inclined to regard its occurrence not as normal, 

 but rather as pathological ( Fleinmiug, '• Amitotische Kernteilung- im 

 Blasenepithel des Salamanders,"' Archiv f. uukr. Auat. Bd. 34, 1890). 



t The secretion of milk is allied to glandular secretion, yet we cannot 

 regard the milk-cells as typical ghmd-celis, for the body and the nucleus 

 of the cell are not appreci ihly enlarged. Nissea (^Archiv f. miki-. Auat. 

 Bd. 26, 1886) writes as follows on the subject of milk-cells : — " In 

 hundreds of preparations I have not been able to detect mito.-es, in spite 

 of the fact that multiplication of the nuclei is an extremely freijiient 

 occurrence. Perhaps, therefore, direct nuclear division takes place in this 

 case. However this may be, the nuclei lying at the inner end of the cell 

 separate from the epithelial cells surrounded by a portion of proto- 

 plasm." 



§ Korschelt ('' Ueber die Bedeutung des Kerns fur die tierische ZiUe," 

 Sitzungsber. der Gesellschaft nnturf. Freuude zu Berlin, 1887, p, 127) 

 writes : — " It is highly remarkable that the bulky nuclei . . . occur pre- 

 cisely in cells which have a secretory function. This may point to the 



Ann. cf; Mag. N. Hist. Ser. 6. Vol. viii. 2b 



