150 



ISTHODUCTION TO CYTOLOGY 



According to Bonnevie (1908, 1911) the chromosomes of Allium, 

 Ascaris, and Amphiuma each give rise to an endogenous spiral thread 

 during the telophases, this spiral thread persisting through the resting 

 stages until the next prophase, when it again condenses to form a chromo- 

 some (Fig. 54, B). In his work on Salamandra Dehorne (1911) asserted 

 that each chromosome is represented at telophase by two interlaced 

 spirals arising from an anaphasic split, and further that these double 

 structures are associated in pairs and persist in this condition through 

 the resting stages. These two conceptions have been criticized by 

 Gregoire (1912), Sharp (1913), and de Smet (1914), who have inter- 

 preted such appearances as occasional aspects of the alveolized chromo- 

 somes without the significance attributed to them by Bonnevie and 

 Dehorne. 



H 





f^ 





& 



& 



■'7 ■ 



Fig. 51. — Somatic mitosis in Tradescanlia virginiana: 

 phase and resting stage (/, K), and early prophase (L, 

 1920.) 



late telophase (H, I), inter- 

 M). X 1900. {After Sharp, 



In the young telophasa nucleus the chromosomes may become ar- 

 ranged in the form of a more or less continuous daughter spireme which 

 is then transformed into the resting reticulum. This spireme stage, 

 however, is not a necessary one; its absence is being reported with 

 sufficient frequency to throw much doubt upon the view that it is a 

 phenomenon of even general occurrence. 



The nucleolus usually makes its appearance during the early telophase 

 as a small droplet or as several such droplets which may later flow 

 together. It seems to have little direct connection with the chromo- 

 somes, but there can be no doubt that its appearance is closely associated 

 with their physiological activities. 



As the telophasic changes proceed the chromosomes with their 

 anastomoses gradually form a more and more uniform reticulum, in 



