314 KOFOID AND SWEZY. 



Binary Fission in Trichomonas augusta. 



This occurs by mitosis in which we may distinguish phases com- 

 parable with tliose in metazoan cell division in the nature and results 

 of the processes carried on in nucleus and cytoplasm, but differing 

 somewhat in their respective chronologies, in minor details of arrange- 

 ment and in relative development of the achromatic organelles, from 

 mitosis in the metazoan cells. 



JMoreo^'er, the sequence of changes in the individual parts of the 

 organism does not proceed with the same relative rapidity in every 

 division. The extranuclear structures especially exhibit a considera- 

 ble variation in this respect. The parts are also mobile in the cyto- 

 plasm to a high degree with the result that a great diversity of pictures 

 of the process of mitosis is here presented. 



The prophase (PI. 1, Figs. 2, 3, 5, 7-10, PI. 2, Figs. 11-12) is that 

 in which the chromosomes are organized out of the karyosome and 

 chromatin network of the nucleus. The organization of the spindle 

 is here much simpler than in the Metazoa and also progresses less 

 rapidly than that of the chromosomes. 



The first indications of mitosis appear in the development of a 

 diffuse intranuclear chromidial cloud (PI. 1, Figs. 2, 3, 5, 8) which 

 fills the nucleiis and is not easily removed by decolorization. Follow- 

 ing this stage this intranuclear material disappears and the chromatin 

 of the nucleus is aggregated in a ragged tangled chromatin thread or 

 skein (PL 1, Fig. 9) Ijnng in the now unstained nuclear sap. Sur- 

 rounding the nucleus at this stage is a halo formed by a vacuole-free 

 zone of fine granular perinuclear cytoplasm which stains more deeply 

 here than elsewhere. At the same time the number of axostylar 

 chromidia has considerably increased (PI. 1, Figs. 5, 9) and the first 

 cytoplasmic chromidia have made their appearance. This extra- 

 nuclear cloud has been previously noted only by Bensen (1909) in 

 T. vaginalis, though he does not connect it with chromidial formation, 

 and by Alexeieff (1914a) casually in T. sanguisuc/ae. It later dis- 

 appears entirely as the chromidia in axostyle and cytoplasm increase 

 in numl)er. 



Individuals in this stage are generally rounded up, and are often 

 large, though mitosis is by no means confined to large cells (cf. Figs. 

 24 and 29). When small ones divide they also round up. The 

 axostyle is more or less withdrawn within the cytoplasm in these 

 rounded stages and is often much curved in fixed material, evidently 



