104 BIOLOGY OF THE PROTOZOA 



In other ciliates the massive micro-nucleus gives rise to a group 

 of chromatin granules which form an umbrella shape mass at one 

 pole of the nucleus (Didinium, Oxytricha, Euplotes, Uroleptus, etc.). 

 This has been described as the "candelabra" stage by Collin (Ano- 

 plophrya) or the "parachute" stage by Calkins {Uroleptus). The 

 number of granules is much larger than the number of chromosomes 

 of the later reducing division, but this large number is halved at 

 the first meiotic division (Fig. 32, p. 64). With the second division 

 the remaining granules usually fuse to form the diploid number of 

 chromosomes and this number of chromosomes is finally reduced 

 to one-half. At the third division these resulting haploid chromo- 

 somes become granular and are divided transversely. 



B. Derived Organization; Cytoplasmic Changes. — 1. Cytoplasmic 

 Chromatin. — During the metabolic activities of the cell, substances 

 which are undoubtedly derived from the nucleus are cast off into 

 the cytoplasm. The majority of these are not represented by 

 demonstrable structures of the cytological organization. Thus in 

 Uroleptus (mobilis and halseyi) fully one-third of the macronuclear 

 chromatin is shed into the cytoplasm at each division and disap- 

 pears as chromatin, while in ciliates generally the entire substance 

 of the macronuclei and a variable proportion of micronuclear 

 substance (fifteen-sixteenths in Uroleptus mobilis) is absorbed in 

 the cytoplasm at periods of conjugation. In the latter case, again, 

 this nuclear substance cannot be definitely traced into cytoplasmic 

 structures (see, however, the described origin of mitochondria in 

 Uroleptus halseyi, p. 75). 



Secondary nuclei which are formed in the cytoplasm of Foramini- 

 fera, Radiolaria and some ameboid forms are traced directly back 

 to nuclear chromatin. Thus in Polystomellina crispa, Peneroplis and 

 other foraminifera the nuclei fragment distributing quantities of 

 chromatin granules (chromidia) in the cytoplasm. These granules 

 in groups of two or three form minute secondary nuclei, one such 

 nucleus in each swarm spore (amebula) which then develops into 

 a megalospheric generation with hundreds of small nuclei formed 

 by division (see p. 69). When mature the protoplasm breaks up 

 into swarms of flagellated gametes, each with one of these minute 

 nuclei (Schaudinn, Lister, Winter et at.). 



The testate rhizopods secondary nuclei develop from chromidia 

 which form the nuclei of ameboid swarmers {Centropyxis Schaudinn, 

 Arcella). Similarly in pseudopodia-forming flagellates (Rhizomas- 

 tigidae) Goldschmidt (1905) describes the formation of secondarj' 

 nuclei in Mastigella and Mastigina (Fig. 45, p. 88) from the cyto- 

 plasmic chromidia. 



2. Cytoplasmic Kinetic Elements. — It is in the cytoplasm that 

 kinetic elements are most highly differentiated, and the often 

 perplexing structures which appear in different types of Protozoa 



