THE (;krm-plasm 



^7 



So far I have not touched upon the question as to what 

 observable parts of the idioplasm are to be regarded as ids. 

 This point cannot be decided with certainty at present, but I 

 have elsewhere expressed the opinion that those rod-like, loop- 

 like, or granular masses of chromatin in the nucleus, — the 

 chromosomes, — are to be considered equivalent, not to single 

 ids, but to series or aggregations of ids. I have therefore pro- 

 posed to call the chromosomes idants} in order to keep up a 

 certain uniformity in the nomenclature. It is probable that the 

 ids correspond to the small granules hitherto called ' microso- 

 mata,' which are known to form the individual idants in many 

 animals : we may mention as an example, Ascaris uiegalocephala^ 

 as in it the nuclear structure is best known. 

 These microsomata, although lying very 

 close together in one row, are nevertheless 

 separated by a thin layer of intermediate 

 substance ; the whole idant cannot there- 

 fore be equivalent to one id. for the latter 

 is a clearly defined vital unit possessing a 

 fixed architecture, and cannot consist of 

 completely separated parts. 



The great variety as regards size, number, 

 and form of the chromosomes in different 

 species of animals, indicates that they pos- 

 sibly have not always a similar morpholog- 

 ical value. As however there is no reason for assuming that 

 the number of ids must always be the same in all species, and 

 as, on the contrary, it is much more probable that their number 

 varies greatly, it is impossible to make use of the above fact as 

 a decisive argument. We can only state that the individual 

 chromosome or idant in all probability represents a different 

 number of ids in different species. 



Division of the nucleus depends on the longitudinal splitting 

 of the idants, in which process each of the spherical ids — assum- 

 ing these to correspond to the microsomata — becomes halved. 

 Each half then becomes rounded off, and passes, together with 

 the idant to which it belongs, into one of the two daughter-nuclei. 



In the ordinary process of cell-division in tissues, which 

 results in the formation of daughter-cells similar to those from 



Fig. 2. 



Two Idants with thei> 

 contained Ids of As' 

 carts tnegalocephala. 

 (After Boveri.) 



1 ' Amphimixis,' pp. 39, 40. 



