380 Naohide Yatsii. 



centrioles. By this time the germ-iiuclei fuse. Ceiitrosome III 

 (that is, the first cleavage centre) appears in the now degenerating 

 centrosonie 11.^^ Centrosome III enlarges a great deal and in it 

 centrosonie IV is formed. This becomes the centre of the second 

 cleavage mitosis. This cycle agrees with Vejdovsky and Mrazek's 

 observation on the egg of Glossiphonia (Clepsine). That the fourth 

 centrosome hecomes the centre of the second cleavage, is, I think, 

 an almost universal phenomenon during the early development of 

 animal eggs. 



IV. Rays and Spindle. 



(a) Terminology. 



Throughout the present paper, I shall use the terms in the fol- 

 lowing sense: 



Pole rays — the entire group of rays radiating from the astral 

 center (Rhumbler). 



Polar rays — rays found in the region of the "cone antipode" 

 (Rhumbler). 



Intermediate rays — rays found between the polar and equatorial 

 rays. 



E(]uatorial rays — rays near the division plane of the cell 

 (Rhumbler). 



Sheath rays — spindlc-like sheath surrounding the spindle formed 

 by the fusion of the equatorial and a part of the intermediate 

 rays. 



Sheaf rays — rays laid down parallel to the spindle in the future 

 cleavage plane ("gerbe de separation," Bouin). 



Spindle = central spindle ; "central" is dropped, because it is 

 sometimes found outside the chromosomal fibers, e. g., Bhynchelmis 

 (Vejdovsky and Mrazek, '03, Fig. 46). 



Chromosomal fibers = "Zugfasern" = Mantle fibers. 



^'Kost.inecki compares the foniiatlon of centrosome III after the "pause" 

 with the reai»pearance of rays after the treatments of cooling, etherization, 

 etc. ('00, p. 0.5). It might he worth pointing out that tliese two plienomena 

 are of entirely different nature: in the former a newer aster ni)i)ears within the 

 old, while in the latter the very same aster hecomes visihle. 



