522 BIOLOGY OF THE PROTOZOA 



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. 36, p. 78). 



2. Phase B. The First Meiotic D iris ion.— 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 (1S89) 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 8 or 9 chromo- 

 somes in Paramecium aurelia basing his view not on the chromo- 

 somes but on the number of fibers which he could distinguish in 

 the connecting strand between the two daughter nuclei. Later 

 observers have found that the number in all species of Paramecium 

 is much greater than this running up to more than one hundred. 

 Dehorne (1920) on the other hand, finds no chromosomes at all, 

 the chromatin being in the form of a continuous single looped 

 thread which divides by transverse division (Fig. 214. Cf. Fig, 215). 



In more favorable types of ciliates than Paramecium the number 

 of chromosomes has been made out with some degree of accuracy. 

 Prandtl (190(')) found lb in Didlnium nasatum (Fig. 216). Prowazek 

 (1899) was a little in doubt whether there were 12 or 13 in the 

 nuclei of Bursaria truncatella, but described () chromosomes in 

 StyJouyrhia pustuJaia. Stevens (1910) described 4 chromosomes in 

 Boreria suhci/rlindrlca l)Ut gave no details of their formation or 

 reduction. Enriques (1908), confirmed by MacDougall (1925) 

 found 4 in Chilodon unciuatus; Popoff (1908) 16 in Carchesium 

 polyinnum; Enriques (1907), the same number in Opercularia 

 coarctata, and Collin (1909), 6 chnmiosomes in Anoplophrya bran- 



chiarum. ^ • • p 



Hamburger (1904) is a bit hazy in her account of the origui of 

 the chromosomes in Paramecium bursaria. The late stage in the 

 crescent is regarded by her as a spireme from which the chromosomes 

 are formed as short curved or V-shaped rods. Calkins and Cull 

 (1907) found that the chromosomes of Paramecium caudahim are 

 derived from a synezesis stage which precedes the crescent and that 

 the chromosomes are already divided at the stage which had 

 generally been regarded as the metaphase. According to this 

 account' the metaphase stage occurs during the metamorphosis 

 of the crescent into the spindle so that the latter when formed is 

 in the early anaphase stage (Fig. 215). Dehorne (1920) thinks 

 these chromosomes are due to cutting of the coiled thread by the 



knife. 



In other ciliates the chromosomes are formed by the union of 

 chromomeres which are derived by fragmentation of the ht)mogene- 



