126 PROTOZOOLOGY 



the centriolc has been r('])()rte(l in many others, such as Hart- 

 mannella (Arndt), Euglypha, Monocystis (Belaf), Aggregata 

 (Dobell, Belaf, and Naville), various Hyi)ermastigina (Kofoid; 

 Duboscq, Grasse; Kirby; Cleveland and his associates). 



In numerous species the division of the centriole (or blepharo- 

 ])last) and a connecting strand between them, which have been 

 called desmose, centrodesmose or paradesmose, have been ob- 

 served. According to Kofoid and Swezy (1919), in Trichonympha 

 campanula (Fig. 56), the prophase begins early, during which 52 

 chromosomes are formed and become split. The nucleus moves 

 nearer the anterior end where the centriole divides into two, be- 

 tw^een which develops a desmose. From the posterior end of each 

 centriole, astral rays extend out and the split chromosomes form 

 loops, pass through "tangled skein" stage, and emerge as 26 

 chromosomes. In the metaphase, the equatorial plate is made up 

 of V-shaped chromosomes as each of the split chromosomes are 

 still connected at one end, which finally becomes separate in 

 anaphase, followed by formation of two daughter nuclei. 



As to the origin and development of the achromatic figure, 

 various observations and interpretations have been advanced. 

 Certain Hypermastigina possess very large filiform centrioles 

 and a large rounded nucleus. In Barbulanympha (Fig. 57), 

 Cleveland (1938) found that the centrioles vary from 15 to 30/x 

 in length in the four species of the genus which he studied. They 

 can be seen, according to Cleveland, in life as made up of a dense 

 hyahne protoplasm. When stained, it becomes apparent that the 

 two centrioles are joined at their anterior ends by a desmose and 

 their distal ends 20 to 30^ apart, each of which is surrounded by a 

 special centrosome (a). In the resting stage no fibers extend from 

 either centriole, but in the prophase, astral rays begin to grow 

 out from the distal end of each centriole (6). As the rays grow 

 longer (c), the two sets soon meet and the individual rays or 

 fibers join, grow along one another and overlap to form the 

 central spindle (d). In the resting nucleus, there are large irregular 

 chromatin granules which are connected by fibrils with one an- 

 other and also with the nuclear membrane. As the achromatic 

 figure is formed and approaches the nucleus, the chromatin be- 

 comes arranged in a single spireme imbedded in matrix. The 

 spireme soon divides longitudinally and the double spireme 

 presently breaks up transversely into paired chromosomes. The 



