NUCLEI AND KINETIC ELEMENTS 



81 



astrosphere, form attraction centers, not only for the spindle fibers, 

 but also for astral rays extending into the cytoplasm. 



3. Nuclei with Pole Plates and Without Endohasal Bodies. — This 

 type of nucleus is characterized by the entire absence of endobasal 

 bodies. A hyaline mass, which stains with difficulty, may, however, 

 be present at the spindle poles during nuclear division, but in 



Fig. ZS.—Bodo lacertce Grassi; division stages continued. (E) Origin of centriole 

 in the nucleus, and their retention in the daughter nuclei, (F to G); (hb) basal bodies 

 (c) centriole. (After Belar.) 



many cases it cannot be detected in the resting nucleus. During 

 division it occurs in characteristic forms known as pole plates. 



In the micronuclei of Paramecium caudatum such a mass forms a 

 hyaline cap at one pole of the otherwise chromatin-filled resting 

 nucleus. Observations are entirely lacking in regard to division 

 of this mass during reproduction, but similar aggregates of non- 

 staining substance are present at the distal ends of the daughter 

 6 



