372 Dr. H. E. Ziegler on Amitotic Nucha)- Divis'on 



the theoretical views which may be brouglit to bear on the 

 point. Bnt Frenzel continues : — " while tlie specific f>;land- 

 cells of tlie pits multiply by the method of indirect (mitotic) 

 nuclear division." Frenzel considers, therefore, that the 

 epithelial cells multiply by amitotic division, the gland- eel Is 

 by mitosis, and this view stands in abrupt contradiction to the 

 statements above. The state of the case is very easily 

 explained when we consider that the cells of the pits, which 

 divide by mitosis, furnish not the slightest grounds for being 

 regarded as gland-cells; the body of the eell is small and 

 contains no drops of secretion. Much more light is conse- 

 quently thrown upon the matter by regarding the pits not as 

 glandular, but as regenerative, and assuming that the '' true 

 epithelial cells " are regenerated and thrust forward there- 

 from. In Periplaneta orientalis, L., T have by the study of 

 sections convinced myself of the justice of this view. 



We should therefore have no grounds tohatever for the assump- 

 tion, loere ice to conclude that in the intestinal canal of Crustacea 

 or Insects the multiplication of cells is based upon amitotic 

 nuclear division, and it appears^ on the contrary, that amitotic 

 nuclear division only occurs in such cells as are in the act of 

 functioning as gland-cells and which sooner or later will 

 perish in so doing. It m.ay here be also mentioned that in 

 many Arthropods there takes ])lace at a certain time a shedding 

 of the whole glandular epithelium of the mid-gut. According 

 to Bizozzero (Atti della K. Accad. d. Sc. di Torino, vol. xxiv. 

 1888-89, p. 702) in Ilydrojihilus piceus the whole epithelium 

 of the mid-gut is shed every two to five days, and the new 

 epithelium is formed from the " intestinal glands " (regene- 

 ration pits) by protrusion and metamorphosis of the cells. 

 In Poly desm ids it was observed by O. vom Rath * that 

 during ecdysis the epithelium of the mid-gut is shed and 

 regenerated. In Hymenoptera the epithelium of the mid-gut 

 is renewed during the pupa state [vide Frenzel, loc. cit. 

 p. 257). The dissolution of the existing mid-gut epithelium 

 in the pupa stoge of the Muscid* has long been known owing 

 to the fundamental investigation of Weisniann f, and the 

 development of the new epithelium has recently been described 

 by Kowalevsky \ and van Rees §. The latter writes as 



* O. vom Eatb, " Leber die Fortpflanzung der Diplopoden (Chilo- 

 gnathen)," Berichte der uaturf. Gesellschat't zu Freiburg i. B., Bd. \., 

 1690, p. 13. 



t A. Weismann, " Die nacbenibryonale Entwicklung der Musciden,'' 

 Zeitsclirift f. wiss. Zoologie, 14 Bd., 1804, 



X A. Kowalevsky, " Beitiage ziir Kenutuis der nacbembryonale Ent- 

 TvickluDg der Muscideu," Zeit.-chr. f. wiss. Zoologie, 45 Bd., 1887. 



§ J. van llees, " Beitiage zur Kenutnis der innern Metamorphose von 



