520 



BIOLOGY OF THE PROTOZOA 



different from somatic mitoses. In different species of Paramecium 

 {cavdatnm, aurelia and bursar ia) a typical prophase stage occurs 

 in the form of a crescent derived from the homogeneous micronucleus 

 which first draws out in the form of a k)ng cyhnder (Fig. 214). 

 In Chilodon uncinatus the micronucleus draws out into a long comma- 

 shaped band and in Cryptochilum nigricans (Maupas, 1889) Vorti- 

 cella monilata and Vorticella nebvUfera (Maupas) and in Opercnlaria 

 coarctata (P^.nriques, 1907) a similar chromatin rod extends in some 

 cases the entire length of the cell. 



Still another type of prophase, the "candlelabra" (Collin, 1909) 

 or "parachute" nucleus (Calkins, 1919) is found in Onychodromns 

 grandis (Maupas), Bursaria truncatcUa (Prowazek, 1899), Didinivm 



Fig. 214. — Micronucleus of Paramecium caudalum in the prophases of the first 

 meiotic division. A, Early stage in the formation of chromosomes; B, elongation of 

 the nucleus prior to crescent formation; C, metaphase of the first division. Dehorne 

 describes the entire chromatin aggregate as forming one highly convoluted chromo- 

 some. (After Dehorne.) 



7iasvtvm (Prandtl, 1906), Anojtlophrya hranchiarum (Collin, 1909) 

 Oxytricha fallax (Gregory, 1923) and Urolephis mobilis. In these 

 cases the nucleus swells to two or three times the usual diameter 

 with the compact chromatin at one pole (Figs. 36, 227). In Urolep- 

 tus mobilis there is an endobasal body within the nucleus; this 

 divides, one-half passing to the periphery of the nucleus at the pole 

 opposite the chromatin mass while the other half remains with the 

 chromatin (Fig. 36). The distal centrosome is the focal point 

 of the spindle fibers which spread out from it to the fragmenting 

 chromatin mass and forms one pole of the mitotic spindle. 



In the transformation of the crescent type of prophase Maupas, 

 Hertwig and Hamburger all agree that the spindle is formed by the 



