214 BIOLOGICAL LECTURES. 



remainder of the nucleus and the re-formation of the daughter- 

 nuclei, while the chromosomes disintegrate into granules which 

 again form the large chromatin reservoirs characteristic of 

 Noctiluca. 



It is hardly necessary to point out further the similarity 

 between this division figure and the mitotic figure of the first 

 type given above. The centrosome within the sphere, the 

 mantle fibers and their insertion in the chromosomes, the ori- 

 gin of the central spindle from the substance of the sphere, are 

 features which are obviously common to the two types. 



The mitotic figure, in all cases, can be easily divided into two 

 portions, of which one consists of chromatin, the other of cen- 

 trosome and spindle fibers. The two parts have more or less 

 separate antecedent phases, and are brought in contact only 

 during the metaphase and later stages of division. It is possi- 

 ble, therefore, to conceive the two processes unequally devel- 

 oped ; a high grade of chromatin and chromosome development 

 may accompany a relatively slight achromatic specialization, and 

 vice versa. In the Protozoa, specialization of the two parts is 

 not synchronous, and the types which are used to demonstrate 

 the successive stages in chromosome formation cannot be used, 

 in the same order at least, for the successive stages in achro- 

 matin differentiations. It is, therefore, more satisfactory to 

 consider the two lines separately. 



Beginning with the chromatin changes, it has been shown 

 that in Noctiluca the chromatin reservoirs disintegrate into 

 smaller and smaller pieces prior to division, and that these 

 small parts are secondarily united into chromosomes. In many 

 of the simpler Protozoa, notably in the Phytoflagellates, in Fo- 

 raminifera (Schaudinn) and Sporozoa (Siedlecki), the chromatin 

 material is aggregated into a single chromatin reservoir which 

 can be compared with one of the eight or ten similar structures 

 in Noctiluca. Rhumbler ('94) 1 described a varying number of 

 chromatin reservoirs (Binnenkorper] in the foraminifer Sacca- 

 mina spkcerica, from one in the smaller forms to three hundred 

 in the larger nuclei. Gromia and other reticulates have a vary- 

 ing number of similar masses (F. E. Schultze). In many cases 



1 Zeitschr.f. wiss. ZooL, Bd. Ivii. 



