PROTOZOAN NUCLEI. 389 



Aberrant Types of Protozoan Nuclei/ 



While nuclei of the type described above in flagellates seem 

 to lead by gradual stages into more complicated forms of the 

 Metazoan type, other nuclei of the Protozoa seem to have de- 

 veloped along a divergent path and finally resemble only 

 remotely the primitive forms on the one hand, and the higher 

 forms on the other. These nuclei may be described as aberrant 

 forms, although the number of such forms is probably greater 

 than any other type among the Protozoa. In most cases, 

 however, the structure can be traced back to more primitive 

 forms of the " Intermediate type." A few examples which 

 have come uncier my own observation must suffice. These are 

 Amoeba proteus among the Rhizopoda, Ccratiinn and Pcridinhon 

 among the Dinoflagellata, Noctihica, a Cystoflagellate, and Sty- 

 lonychia among the Ciliata. 



Amoeba proteus (Fig. i6). The nucleus of this common 

 rhizopod is of large size and of characteristic shape, resembling 

 a biconcave disc. It is constant in shape and is bounded by a 

 firm membrane which, together with the granular chromatin 

 contents, can be easily made out while the animal is alive. The 

 finer structure, however, is seen only in sections which, with these 

 large forms, can be cut in any desired plane. The nucleus 

 contains, in addition to the general ground substance, or nuclear 

 sap, two kinds of staining substances one of which becomes 

 intensely black with iron ha^matoxylin, while the other is gray. 

 The more deeply staining substance is chromatin in the form of 

 granules distributed throughout the nucleus ; the other sub- 

 stance has the form of a disc lying in the center of the nucleus. 

 Gruber ('83) calls this central mass the "nucleolus." In all of 

 the specimens which I examined at this time the nucleus had 

 the same structure and I am convinced that it is typical of 

 Amoeba proteus. The faintly staining central mass is perfectly 

 homogeneous in structure and, although I have not seen it in 

 division, I am confident that it is to be compared with the intra- 

 nuclear body in the flagellates. In other species of Auuvba the 

 nucleus possesses an internal structure similar to the " nucle- 

 olus centrosome " of Euglena (Schaudinn, '94). 



Annals N. Y. Acad. Sci., XI, October 13, 1898—26. 



