125 



to determine positively that the nuclei in Fig. 21 are the result of 

 direct division, yet the flattened side of the upper nucleus strongly 

 supports this view. There can be no question as regards the mitotic 

 division of the lower nucleus (Fig. 21b), for fifteen chromosomes are 

 clearly seen, and the nuclear membrane has already begun to dis- 

 appear. In Fig. 22 the cytoplasmic constriction is about to effect a 

 complete division, and it is no longer possible to determine the method 

 by which the two nuclei have divided. From what has been said above, 

 however, one is justified in concluding that these nuclei are the result 

 of direct division. 



The above data show conclusively that amitosis plays an important 

 role in the development of the pigeon's blastoderm. The idea that 

 the cells which divide by amitosis are on the road to degeneration 

 receives no support whatever from these studies, for it can not be said 

 that the material is in any way pathological. The fact that amitosis 

 is found intimately associated with mitosis would alone exclude this 

 possibility. 



Since, as I have shown, mitosis may follow amitosis, and vice 

 versa, it seems very probable that amitosis is the result of special 

 physiological conditions, which create a stimulus to cell-division. Just 

 what these conditions are, we are, of course, unable to say, but what- 

 ever factors are involved in bringing about the rapid growth of any 

 region would seem to be concerned in causing amitosis. 



Hull Zoological Laboratory, University of Chicago, 

 September 15, 1907 (eingegangen am 18. Nov.). 



Nachdruck verboten. 



Zur Entwickeliingsgeschiehte des Schlüsselbeines und der 

 Halsliautmuskulatur bei den Vögeln und im besonderen beim 



KanarienTOgel. 



Von Dr. Wladimir Kulczycki, 

 Professor der K. K. tierärztlichen Hochschule in Lemberg. 



Seit den von mir in den Jahren 1901 und 1903 veröffentlichten 

 Ergebnissen über die Entwickelung des Schlüsselbeines beim Huhn, 

 Taube und Ente^) wurden keine weiteren Untersuchungen in dieser Rich- 



1) Zur Entwickelungsgeschichte des Schultergürtels bei den Vögeln 

 mit besonderer Berücksichtigung des Schlüsselbeines. Anat. Anzeiger, 

 Bd. 19, 1901, p. 577—590, und Kosmos, Lemberg, Bd. 28, 1903, 

 p. 44—66. 



