No. 3] THE PROTOZOA AND METAZOA. -J I J 



network in Noctiluca, and "karyosomes" here represent the 

 entire chromatic reticulum of metazoan cells. Karyosomes are 

 characteristic of many Protozoa, and the nuclei containing them 

 are classed together by Gruber ('84) as the " vesiculate " type 

 (" Blaschenformige "). In all such nuclei a membrane, nuclear 

 ground substance, or " sap," and one or more central granules 

 of chromatin can be distinguished. 



In Noctiluca the two nuclear substances differ widely in their 

 affinity for dyes, the oxychromatin being stained a clear and 

 intense red by the Biondi-Ehrlich mi.xture, while the basichro- 

 matin is stained a brilliant green. This difference in color is 

 so marked, and the limits of the two substances so distinct, 

 that the smallest particles of green basichromatin can be easily 

 detected on the red background of oxychromatin. This stain 

 is, therefore, invaluable in following the chromatin changes 

 during nuclear activity. 



In addition to the basichromatin and oxychromatin, a small 

 spherical body (x) surrounded by a hyaline area (Figs. 3, 4, 6, 

 and 7) is usually to be found in the nucleus. With iron haema- 

 toxylin and orange it takes an even more brilliant haematoxylin 

 stain than the chromatin, remaining black or blue while the 

 karyosomes are a deep gray. I have not succeeded in staining 

 it successfully with the Biondi-Ehrlich mixture. In most rest- 

 ing nuclei only one such body is present. From the subse- 

 quent changes in the nucleus, and from analogous bodies in 

 other Protozoa, there is some reason to regard this corpuscle 

 as the centrosome. 



B. The Sphere in the Resting Cell. 



In the cytoplasm, outside of the resting nucleus, lies a large 

 cytoplasmic mass which was first pictured by Allman ('72) and 

 later described by Robin ('78) as a nucleus. From its relation 

 to the nucleus and its behavior during cell division this cyto- 

 plasmic mass may be called the "attraction-sphere" or simply 

 the " sphere," although in its resting stage no centrosome can 

 be found in it. It is often as large as or larger than the nucleus 

 (Figs. I and 8), but differs in appearance at different stages. It 



