in the Animal Kingdom. 369 



The epithelium of the urinary bhadJev of different mammals, 

 especially the mouse and the dog, has recently received a 

 minute investigation at the hands of A. S. Dogiel, who writes 

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

 lium we find amitotic nuclear division in the cells of the upper 

 laj^ers, and mitotic in those of the remaining layers." " In 

 different mammals, but chiefly in the small Rodents, tlie 

 uppermost epithelial cells of the urinary bladder are of an 

 extraordinary size, and j)0ssess a harge number of nuclei." 

 " We see that the process of multiplication of the nuclei in 

 the epithelial cells of the uppermost layers is similar to that 

 which is found in the giant cells^ leucocytes, epithelium of 

 the nnammary glands, &c., namely direct amitotic nuclear 

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

 The uppermost cells of the epithelium of the urinary bladder 

 have 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 further 

 reflect that in multilamellar epithelia the uppermost layer of 

 cells always undergoes a gradual degeneration and is regene- 

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

 amitotic nuclear division before us the biological conditions 

 are perfectly typical f. 



In cells which are typical gland-cells amitotic division of 

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

 secretion takes place always have a considerable balk and 

 usually a large tiucleus^^ which never divides by mitosis' 



* A. S. Dogiel, " Ueber das Epithel der Harnblase,"' Archiv f. mikrosk. 

 Anatomie, 35 Bd., 1?590. 



t Amitotic nuclear division in the epithelium of the bladder ha^ been 

 found not only in Mammals, but also in Urodela. Flamming observed it 

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

 but rather as pathological (Flemming, " Amitotische Kernteilung im 

 Blasenepithel des Salamanders," Archiv f. mikr. Anat. Bd. 34, 1890). 



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

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

 of the cell are not appi'eci.ibly enlarged. Nissen (Archiv f. mikr. Auat. 

 Bd. 20, 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 tJie nuclei is an extremely frequent 

 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 trom the epithelial cells surrounded by a portion of proto- 

 plasm." 



§ Korschelt (" Ueber die Bedeutung des Kerns fiir die tierische Zslle," 

 Sitzungsber. der Gesellschaft miturf. 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. J'his may point to tlie 



Ann. <^; Mag. N. Hist. Ser. 6. Vol. viii. 25 



