NUCLEAR DIVISION OF NOCTILLX'A. 245 



poles of tbe nucleus, the probability is very greatly in favour 

 of the first atternative, although the mass is not so bulky or so 

 well marked off as in other Protozoa. But, if it really repre- 

 sents the pole-plate, what then are we to say of the large ex- 

 tranuclear archoplasm, whose nature and ideutity with the pole- 

 plate were discussed at some length in my former paper ? I 

 hold the view that the nucleoplasm, /. e., the mass above re- 

 ferred to, and the archoplasm are to l)e looked upon as together 

 the equivalent of the pole-plate. In other words, the pole-plate, 

 otherwise situated entirely within the nucleus, has, in Xocliluca, 

 come to lie for the greater part in the cytoplasm, with only a 

 small portion of it, therefore, left within the nucleus. 



But tlie most interesting point here to be observed is that 

 which has been discussed by B. Hertwig, first in his lecture 

 " Ueber Befruchtung und Conjugation " in 1892 ('92, a), and 

 then in his second lecture " Ueber Centrosome und Central- 

 Spindel " in 1895 ('95). In these lectures he tried to show 

 that, in the nuclear division of a Protozoan, the active part is 

 played within the nucleus and that the entire achromatic spindle 

 of a Protozoan nucleus corresponds to the central spindle plus 

 the centrosome of a Metazoan, a view first propounded by ]M. 

 Heidenhain ('94, d). But the case is otherwise, as I have 

 first shown in 1891 ('91, a), and this activity in the nuclear 

 division of JVoctihica does not take placu within the nucleus, 

 but entirely outside it. Further, I have often found that there 

 is in the cytoplasmic mass, differentiated from the rest and 

 identified by me with the archoplasm of Bovert, a small sphe- 

 rical body which undoubtedly represents the centrosome. I 

 have therefore concluded that (Jystoflagellata in this respect forms 

 an interestin«! connecting; link between the 3Ietazoa and the 



