138 



PROTOZOOLOGY 



pies may be mentioned the chromosomal divisions in Astasia laevis 

 (Belaf), Entosiphon sulcatum (Lackey), and a number of ciliates. In 

 a small number of species observations vary within a species, as, 

 for example, in Peranema trichophorum in which the chromosomes 

 were observed to divide transversely (Hartmann and Chagas) as 

 well as longitudinally (Hall and Powell; Brown). It is inconceivable 

 that the division of the chromosome in a single species of organism 

 is haphazard. The apparent transverse division might be explained 



Fig. 64. Stages in mitosis in Zelleriella inter iriedia, X1840 (Chen), 

 a, early prophase; b, metaphase; c, anaphase; d, telophase. 



by assuming, as Hall (1937) showed in Euglena gracilis, that the 

 splitting is not completed at once and the pulling force acting upon 

 them soon after division brings forth the long chromosomes still 

 connected at one end. Thus the chromosomes remain together before 

 the anaphase begins. 



In the instances considered on the preceding pages, the so-called 

 chromosomes found in them, appear to be essentially similar in 

 structure and behavior to typical metazoan chromosomes. In many 

 other cases, the so-called chromosomes or "pseudochromosomes" 

 are slightly enlarged chromatin granules which differ from the ordin- 

 ary chromatin granules in their time of appearance and movement 

 only. In these cases it is of course not possible at present to deter- 

 mine how and when their division occurs before separating to the 

 respective division pole. In Table 5 are listed the number of the 

 "chromosomes" which have been reported by various investigators 

 in the Protozoa that are mentioned in the present work: 



