296 BIOLOGY OF THE PROTOZOA 



spireme but this is so exceptional among eiliates that it cannot be 

 accepted without confirmation. 



In the majority of eiliates this first meiotic mitosis is markedly 

 different from somatic mitoses. In different species of Paramecium 

 {caudatum, aurelia and bursaria) 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 long cylinder (Fig. 57, p. 103). 

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

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

 cella monilata and Vorticella nebulijera (Maupas) and in Opercularia 

 coarctata (Enriques, 1907) a similar chromatin rod extends in some 

 cases the entire length of the cell. 



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

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

 grandis (Maupas), Bursaria truncatella (Prowazek, 1899), Didinium 

 nusutum (Prandtl, 1906), Anoplophrya braucliiurum (Collin, 1909), 

 Oxytricha fallax (Gregory, 1923), Uroleptus mobilis and halscyi 

 (Fig. 32, p. 64), Euplotes, Turner (1930), Conchophthirius (Kidder, 

 1933). In these cases the nucleus swells to two or three times 

 the usual diameter with the compact chromatin at one pole 

 (Figs. 32, 162). In Uroleptus 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. 32, p. 64). 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 

 shortening of the long axis of the crescent. Calkins and Cull 

 (1907) and Dehorne (1920), however, find that the division center 

 or achromatinic substance which forms the poles of the spindle 

 migrates from its apical position in the crescent to the center of 

 the convex side, and that this new position marks one pole of the 

 spindle (Fig. 147). 



In the parachute type the second pole is formed by the outgrowth 

 from the chromatin mass of a second pole similar to the first, the 

 chromatin granules thus being left in the nuclear plate position or 

 center of the spindle figure (Fig. 32, p. 64). 



2. Phase B. The First Meiotic Division.— Exact knowledge of 

 the formation of chromosomes and their division is scanty, due in 

 part to the large number of chromosomes and to their small size. 

 Maupas (1889) made no attempt to enumerate the chromosomes; 

 nor did he describe their formation beyond the brief account of the 

 fragmentation of the homogeneous chromatin masses of the micro- 

 nuclei. Hertwig (1889) believed that there were S or 9 chromo- 



