REPRODUCTION 131 



In some forms, such as Noctiluca (Calkins), Actinophrys 

 (Belaf), etc., there may appear at each pole, a structureless mass 

 of cytoplasm (centrosphere), but in a very large number of 

 species there appear no special structures at poles and the spindle 

 fibers become stretched seemingly between the two extremities 

 of the elongating nuclear membrane. Such is the condition found 

 in Cryptomonas (Belaf), Rhizochrysis (Doflein), Aulacantha 

 (Borgert), and in micronuclear division of the majority of Euciliata 

 and Suctoria. 



The behavior of the endosome during the mitosis differs among 

 different species as are probably their functions. In Eimeria 

 schuhergi (Schaudinn), Euglena viridis (Tschenzoff), Oxyrrhis 

 marina (Hall), Colacium vesiculosum (Johnson), Haplosporidium 

 limnodrili (Granata), etc., the conspicuously staining endosome 

 divides by elongation and constriction along with other chromat- 

 ic elements, but in many other cases, it disappears during the 

 early part of division and reappears when the daughter nuclei 

 are reconstructed as observed in Monocystis, Dimorpha, Eu- 

 glypha, Pamphagus (Belaf), Acanthocystis (Stern), Chilomonas 

 (Doflein), Dinenympha (Kirby), etc. 



In the vegetative division of the micronucleus of Concho- 

 phthirus anodontae (Fig. 60), Kidder (1934) found that prior to 

 division the micronucleus moves out of the pocket in the macro- 

 nucleus and the chromatin becomes irregularly disposed in a 

 reticulum; swelling continues and the chromatin condenses into 

 a twisted band, a spireme, which breaks into many small seg- 

 ments, each composed of large chromatin granules. With the 

 rapid development of the spindle fibers, the twelve bands become 

 arranged in the equatorial plane and condense. Each chromosome 

 now splits longitudinally and two groups of 12 daughter chromo- 

 somes move to opposite poles and transform themselves into two 

 compact daughter nuclei. In Zelleriella intermedia (Fig. 61), 

 Chen (1936) saw the formation of 24 chromosomes, each of which 

 is connected with a fiber of the intranuclear spindle and splits 

 lengthwise in the metaphase. While in the majority of protozoan 

 mitosis, the chromosomes split longitudinally, there are observa- 

 tions which suggest a transverse division. As examples may be 

 mentioned the chromosomal divisions in Astasia laevis (Belaf), 

 Entosiphon sulcatum (Lackey), and a number of ciliates. In a 

 small number of species observations vary, as, for example, in 



