285_ 



any cases of this kiad. The relative frequency of amitosis and mitosis 

 in this form has not yet been determined. 



Chick embryos. All observers are familiar with the fact that 

 mitosis is not at all uncommon in chick embryos at all stages, but 

 the question as to whether nuclear multiplication is entirely due to 

 mitosis is one which, so far as I am aware, has not been discussed. 



Nos. I— IX in Figure 12 show a few of the cases of apparent 

 amitosis found in embryos of various stages. No. I is from the dorsal 

 ectoderm in the seventh somite of a ten-somite stage; Nos. II and 

 III are from the neural tube in the same region at the same stage; 

 Nos. IV — VI are from the neural tube at eight days; No. VII is 



•'*■..» *' ■ * t*\ rf ■ "* *^ ♦■.\ 



•:i-.v'>-.--.,.:- - Vv I-'» ■•> * '-^J 







* ■ •• ,•■■■* *-* >l:*n 



^'■» » i:^- • -*v^-* •■■■ -'^f^ 









Fig. 11. 



from the seventh mesoblastic somite of the thirteen-somite stage; 

 No. VIII is from the cartilage of the vertebral column at eight days, 

 and No. IX is from the notochord in the stage of thirteen somites. 

 Numerous other similar cases were observed in the various tissues and 

 organs. Nos. Ill represents a condition often found in the neural tube 

 of the stage of ten somites, and perhaps indicating degeneration of 

 one of the products of division or possibly some other process of 

 nuclear transformation. In all cases of this kind one of the nuclei is 

 normal in appearance while the other is small and rounded in form 

 and lies in a space which appears to indicate the previous size and 

 shape of the nucleus but does not possess a visible limiting membrane. 



