No. 3] THE PROTOZOA AND METAZOA. 727 



the daughter-spheres takes place before the daughter-nuclei of 

 the preceding mitosis are completely separated (Fig. 21). Fig. 

 21 also shows that the plane of the second division of each 

 sphere is at right angles to the plane of the first division. The 

 same thing is shown in an earlier stage in Fig. 18, where the 

 primary axis of the daughter-nucleus is bending around the 

 sphere ; and again in the sections represented in Figs. 24, 39. 



In some cases, particularly after fixation with Hermann's 

 fluid, thick but short fibrous processes may be seen passing 

 from the sphere into the cytoplasm (Figs. 9 and 11). These 

 are analogous to the astral rays of metazoan cells, and like 

 the central-spindle fibers they are formed from the substance 

 of the sphere, being made up of granules or microsomes 

 similar to those found in the sphere. 



According to the foregoing description, the sphere in Nocti- 

 liica apparently corresponds to Boveri's archoplasm ('88). It 

 is a persistent cytoplasmic structure, of a definite size and 

 shape in resting and active cells, and appears to consist of 

 a specific substance. Astral rays and central-spindle are 

 formed from its substance, while at certain stages a centre- 

 some lies within it (see p. 731). 



The main observations by contemporary writers on the 

 sphere fall into one or other of two groups, according as they 

 agree with Van Beneden's or Boveri's conception of the origin 

 of this structure. Van Beneden thinks that the sphere, while 

 it consists of the same substance, is morphologically different 

 from the cell plasm. Boveri originally considered it (and 

 with it all spindle and astral fibers) as not only different 

 from the cell plasm morphologically, but as composed of an 

 independent substance — the archoplasm. Among botanists 

 the " archoplasm idea " is generally accepted, and is expressed 

 by Strasburger's term " kinoplasma," while among zoologists 

 this theory has not been generally approved, most observers 

 supporting either Van Beneden's theory or some modification 

 of it. There is, however, the greatest latitude in this support. 

 Many interpret the sphere as formed anew from the cyto- 

 plasmic reticulum at each mitosis. (See among others Heiden- 

 hain ('94), Reinke ('94), Wilson ('95), Eismond ('95), Kostanecki 



