MORPHOLOG Y AND PH YSIOLOG Y 2 1 



groups of the Ciliata, two different nuclei, a macronucleus and 

 a micronucleus, are normally present. The macronucleus is 

 much the larger and controls the metabolic or trophic activities 

 of the organism, while the micronucleus is very minute and is 

 concerned with the reproductive activity. Some species have 

 two or more nuclei of each kind, but the majority possess only 

 one of each kind. In Mycetozoa (Fig. 69), some other Sarcodina 

 such as Actinosphaerium (Fig. 98), Pelomyxa palustris, Proto- 

 ciliata, and numerous Sporozoa, there occur many nuclei of 

 similar structure. These multinucleate forms result either from 

 repeated divisions of a single nucleus or from fusion of numerous 

 uninucleate individuals. 



Although protozoan nuclei manifest various structures they 

 may be put under two types: compact, or massive, and vesicu- 

 lar (Fig. 3). The compact nucleus, which is most frequently 

 found in ciliates, is filled more or less compactly with minute 



Nuclear membrane 

 Endosome 

 Achromatic strand 

 Chromatin granules 



Fig. 3 a. \'esicular nucleus, b. Compact nucleus. 



chromatin granules. The macronucleus of Paramecium cauda- 

 tum represents this type (Fig. 16). The vesicular nucleus con- 

 sists of a nuclear membrane, achromatic strands or network, 

 chromatin granules and nuclear sap. Besides there is an intra- 

 nuclear body, which is usually spherical in form, and which ap- 

 pears to be of different make-up, as judged by its staining reac- 

 tion, among different nuclei. In some it seems to be composed 

 almost exclusively of chromatin, while in others it shows vary- 

 ing proportions of chromatin and plastin materials. This chro- 

 matic body is often called the karyosome, but the use of this 

 term has been attended with much confusion. The term endo- 

 some is, therefore, employed in the present work, in agreement 

 with Minchin and Calkins, to designate one or more conspicuous 

 intranuclear bodies. 



While chromatin granules are usually confined to the intra- 



