VII CHROMIDIA IN PROTISTA 



209 



evidence of qualitative chromatin distribution among the nuclei so formed. 

 Since, however, during nuclear multiplication by means of chromidia 

 the chromatin is resolved into small particles which are not improbably 

 its structural units, it is possible that there takes place a quaUtative 

 sorting out of these units into the new nuclei which are formed by their 

 aggregation into masses. Moreover, in assessing the significance of 

 accounts of nuclear multiphcation through the intermediation of chromidia 

 much caution must be used. It must be remembered on the one hand 

 that the study of the cytology of the Protista is often beset with much 

 greater difficulties of technique than in the case of the Metazoa, owing 

 to the minuteness of the elements concerned. Dobell and Jameson, as 

 the result of their study of Aggregata and Diplocystis, are inclined to doubt 

 accounts of chromidia formation in the Coccidia and Gregarines, such 

 as, for instance, that of Schaudinn for Coccidium schubergi mentioned 

 above. In the anaphase of the first division of the microgametocyte 

 nucleus of Aggregata (the mitosis shown in Fig. 86, C) the chromosomes 

 which were spheroidal in the metaphase become filamentar again. The 

 asters at the two poles of the spindle divide repeatedly, and at each 

 division the chromosomes divide longitudinally, becoming at last ver>' 

 minute. They are finally sorted out in groups of six, each group forming 

 a nucleus at the periphery of the gametocyte cell, there to multiply by 

 mitosis to form the microgamete nuclei. It can hardly be doubted that 

 this process corresponds to the chromidial formation described by 

 Schaudinn as above, a conclusion which suggests that there the term 

 " chromidia " might be translated into " minute chromosomes "—a 

 change in terminology implying that the process of their formation 

 involves an exact division and partition of differentiated elements. 



It must also be remembered that the Protistan nucleus may have a 

 composition very different from that of the Metazoa or Metaphyta. In 

 the latter groups the nucleus always, so far as we know, contains either 

 a single or a double series of differentiated elements (with the special 

 exception of the triploid, tetraploid, etc., nuclei considered on page 150). 

 In the Protista, however, it appears that the nucleus may be polyploid, 

 containing, not one or two, but a great number of series of elements. 

 Examples of such polyenergid nuclei (Hartmann. 1909) are afforded by 

 the great nuclei of the Radiolaria. The nuclear cycle of one of these, 

 Aiilacantha (Borgert, 1901, 1909), is as follows: 



Reproduction may take place asexually by binary fission of the cell, 

 or sexually through the intermediation of gametes. The division of 

 the nucleus in the first type of reproduction takes place by a form of 

 mitosis superficially very similar to a Metazoan mitosis (Kig. 89), but 

 accompanied by the formation of an enormous number of chromosomes. 

 The number of these is far more than a thousand, but varies greatly in 



