SPECIAL MORPHOLOGY OF THE PROTOZOAN NUCLEUS 255 



condenses, there is left a small bud, usually attached by a short 

 peduncle, and this bud, which Siedlecki calls the secondary karyosome, 

 seems to be the seat of the subsequent changes in the disruption of 

 the nucleus. The secondary karyosome enlarges as though a certain 

 amount of chromatin had reached it through the peduncle. When 

 it has reached the volume of the first karyosome, it is also similar 

 in structure. A third karyosome is then formed in the same way, 

 and so on until in some cases more than twenty have been devel- 

 oped. The chromatin of the original body breaks into granules, and 

 in this state penetrates the connecting thread into the daughter-karyo- 

 somes, formed by budding. It is rather difficult to determine the 

 function of this peculiar process, unless with Schneider ('83) and 

 Mingazzini ('92) we assume that it is an antecedent or preliminary 

 phase of spore-formation. Labbe\ on the other hand, regarded the 

 karyosome as a reserve of chromatin which at first contains all the 

 chromatin of the 

 nucleus, and 

 which increases 

 constantly by the 

 addition of other 

 nuclear particles 

 (oxychromatin, ™ B . ,., ■ , „ 



X , J , , , ,. , Fie. i«. — The nucleus and karyosome 111 Atossta ebertlu. 



Labbe, '96), the [Siedlecki.] 



increase going 



into the formation of secondary karyosomes. He considered these 

 phenomena only stages in the "purification" (V epuration) of the nu- 

 cleus, but Siedlecki returns to the view of Schneider and Mingazzini, 

 and shows that they are but preparatory phases of reproduction, in 

 fact the beginning of division of the nucleus, leading to the formation 

 of microgametes or male reproductive cells. 1 



In other groups of the Protozoa, nuclei with one karyosome are 

 somewhat more complicated and obviously of a higher type. The 

 Heliozoa, for example, furnish nuclear types which, at first sight, ap- 

 parently agree with the above forms. The agreement is, however, 

 only superficial ; for although similar in their general features to the 

 nuclei of Sporozoa, they contain achromatic structures lacking in 

 the latter, while their development is altogether different. A distinct 



1 The stages which Siedlecki has described may be briefly outlined as follows : The 

 chromatin network reappears in the vicinity of the membrane, and constantly increases by 

 the addition of the smaller karyosomes. It is then drawn out into long threads and at 

 the same time the nuclear membrane disappears. The karyosomes are almost entirely 

 used up in the formation of these elements, although a small portion remains as the charac- 

 teristic residual mass. The chromatin then collects at the periphery of the cell, where little 

 nuclei are formed, and each nucleus becomes the chief part of a filamentous microgamete 

 (Fig. 127). 



