372 Dr. II. E. Ziegler on Amitotic Nuchar Divis'on 



tlie tliooretical views which may be hrou^jht to Leav on the 

 point. Bnt Frenzcl continues : — " wliile tlie specific fjland- 

 colls of the ])its multiply hy the method of indirect (mitotic) 

 Tiueleav division," Frenzel considers, therefore, that the 

 e])ithelial cells multiyjly by amitotic division, the <i;land- cells 

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

 statements above. The state of the case is very ensilv 

 explained wdien we consider that the cells of the pits, whieli 

 divide by mitosis, furnish not the sliiihtest grounds for beitiu; 

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

 contains )io 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 tinust forward there- 

 from. In Perip^aneta orienta/is, L., I have by the study of 

 sections convinced myself of the justice of this view. 



We should therf'fore have no grounds V'hatever for the assump- 

 tion, were we 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 may here be also mentioned that in 

 many Arthropods there takes ]ilace at a certain time a shedding 

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

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

 1888-89, p. 702) in JiT/drophilus 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 Polydesmids it was observed by O. vom Kath * 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 jiupa stage of the Muscidie has long been known owing 

 to the fundamental investigation of \\ eismann t? '^^^^ the 

 development of the new epithelium has recently been described 

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



* O. vom Eath, " Ueber die Fortj Haiizung der Diplopoden (Chilo- 

 gnathen)," Borichte der iiaturf. Gesellsthalt zu Freibuvfr i. B., Bd. v., 

 1S90, p. 13. 



t A. \\'oismnnn, " Die iiachenibryojiale l"nt-w ickhing dor Miisciden," 

 Zeitsclirift f. wiss. Zoolupe, 14 Bd., IKU. 



\ A. Kowiikvsky, "Bcitiiigo /iir Keiintuis der uaclieiubrvonnle Eut- 

 vicklung diT iMu.sciden/" Zeil.-chr. f. wiss. Zoologie, 4o IM., 18t<7. 



§ J. van KVes, "Beitiage zur KeiiiitniB dev innern Metnniorpliose von 



