366 Dr. II. E. Zicgler on Amitotic Xiichar Division 



division is accompanied by a division of tiie cell, a division 

 of the attraction-sphere takes place. 



Accordin,<:^ to all the investigations whicli have hitherto 

 been made, it is a matter of certainty that those nuclei which 

 divide without initoftis are always distinguished by their 

 excessive size*. This peculiaritv appears also to occur in the 

 case of the leucocyte-nuclei which divide without mitosis, 

 although it is not so noticeable here as elsewhere. The 

 unusual size is undoubtedly connected with the physiological 

 function, and, in my opinion, it is permissible to advance the 

 hy|)othesis that in the Metazoa amitotic nuclear division 

 occurs [chiefly, perhaps exclusively) in such nuclei as minister 

 to a 2)i'ocess of unusually active secretion or assimilation. 

 With regard to this theory, I will now consider a few cases 

 of amitotic division. 



The regressive changes which set in in the egg-cells in the 

 vertebrate ovary take place with the help of leucocytes, which 

 creep into their interior, and of cells which penetrate the outer 

 wall of the egg-cell from the epithelium of the follicle, which 

 has become multilamellar ; the nuclei of the cells which etiect 

 the absorption of the egg-cell degenerate while coatinuing to 

 increase in size, and exhibit amitotic division. The physio- 

 logical conditions iu this instance are the same as in the 

 nuclei in the yolk of merol>lastic Vertebrates, in so far as it is 



* In some cases liirge nuclei of this kind have had the term "giant" 

 applied to them. It woukl be advisable always to employ the same 

 name for all uuu«ually lar^e nuclei occurring in the Metazoa (with 

 the exception of the nuclei of the genital cells). In this sense we 

 could generalize the expression -'giant nucleus." The term macro- 

 nucleus, whicli is employed in speaking of the ciliated Infu<:oria and 

 Acinetaria, should not be transferred to the Metazoa, for, indeed, the 

 Protozoa in question occupy a position quite by themselves with reference 

 to nuclear conditions. For the type of unusually large nuclei which is 

 found in the Metazoa I would propose the name " me</aiiiiclens." Recent 

 discoveries may then be stated very briefly as follows : — Where mega- 

 nuclei occur there takes place a process of active secretion or assimila- 

 tion ; meganuclei can divide without mito.sis, and amitotic nuclear 

 division among the A[etazoa occurs only in meganuclei ; meganuclei have 

 only a limited capacity for division, and always perish after a time. — It 

 woiild be advisable to give the nuclei of the genital cells an exceptional 

 position, and not to include them among the meganuclei. It is true that 

 tiie nucleus of the ovum, adapting itself to the ovogenetic processes, 

 attains an extraordinary size, but its bulk is capable of diminution ; while 

 in the case of a typical meganucleus, so far as we know, mitotic division 

 never again takes place, the nucleus of the ovum undei^oes mitotic 

 division in giving rise to the first directive vesicle. In the nuclei of 

 somatic cells the adaptation to a detinite physiological function could 

 advance so far as to annihilate the normal faculty for division ; in the 

 nuclei of the genital cells tliis naturally could not take place. 



