STRUCTURE OF NUCLEUS , 61 



karyosome, and when it divides it does so by mitosis, while the latter, 

 though developed from a nucleus like the micronucleus, has so changed 

 in appearance and structure that it seems doubtful if it should still be 

 regarded as a true nucleus (Fig. 37). It is sometimes spherical in form, 

 but it is more usually slightly elongated. It may be many times as long 

 as it is broad, and in such cases may have a beaded appearance, as in 

 Stentor and Spirostomvm (Figs. 22 and 509). It may even be irregularly 

 branched, as in certain Suctoria (Fig. 531). It consists of a dense material 

 impregnated with granules which become more evident during division. 

 Vacuoles are often present, while sometimes, as in the species of Colfoda, 

 the elongated macronucleus contains within it one or more deeply staining 

 bodies (Fig. 498). It is evident that the macronucleus differs in many 

 ways from the micronucleus and the nuclei of other Protozoa. During 

 division it does not behave as true nuclei do, and there seems to be 

 little change in its appearance, except for the greater clearness of its 



#1 '0^ ^#^ ^^ 



Fig. 35. — Stages in the First Nuclear Division in the Schizont of Hepatozoon 

 balfouri, showing Division of the Karyosome, which appears to be entirely 

 devoid of Chromatin ( x 6,000). (Original.) 



granules. It is generally assumed that the granules in the macronucleus 

 are chromatin, but, if this be so, there must have taken place a remarkable 

 increase in the chromatin during its formation and growth from the micro- 

 nucleus from which it was originally derived. It seems not impossible 

 that this material is not actually chromatin, but some other substance 

 which has been elaborated to fulfil a special function. 



In this connection it will be necessary to refer again to a theory which 

 was suggested by Schaudinn, and subsequently elaborated by Goldschmidt 

 and others. According to this theory the Protozoan nucleus is constructed 

 of two fundamentally different parts, which in the Euciliata are separated 

 in two distinct nuclei. The one part consists of vegetative material which 

 controls nutrition, movement, and other vegetative functions, while the 

 other is composed of generative material which takes part in the syn- 

 gamic process. This theory has been extended to the chromatin itself, 

 which is supposed to be of two kinds, the one idiochromatin, which takes 

 part in syngamy, and is responsible for the transmission of hereditary 



