Lecture XXVIII. 259 



pellicle with large nuclei distributed in it. No cell-walls have yet been 

 formed and the nuclei are often seen in mitosis. The stimulus for division 

 seems in these cases to advance as a wave across the pellicle so that successive 

 rows of nuclei in the successive stages of mitosis may be observed. 



As these preparations are largely a matter of good fortune in hitting off 

 the exact stage in development, many preparations should be made. A suc- 

 cessful preparation will more than repay the trouble, and affords a record of 

 the minutest details of perhaps the most interesting and suggestive biological 

 phenomenon. 



Even the thicker pellicles, in which cell-division has already taken 

 place, will afford preparations showing many mitoses. In these the details 

 of the process may often be seen with the most astonishing clearness. 



17* 



