538 BIOLOGY OF THE PROTOZOA 



until it occupies fully two-thirds of the cell. It then condenses into 

 a compact homogeneous ellipsoidal nucleus, invisible in the living 

 cell, and stains intensely with chromatin dyes (Fig. 225, 10). It is 

 now ready for the first macronuclear division and divides twice prior 

 to division of the cell. It is perhaps significant that a similar dense 

 ellipsoidal nucleus is formed by fusion of the eight macronuclei 

 prior to cell division in vegetative life (see p. 221). 



An essentially similar history of the amphinucleus occurs in 

 Colpidium colpoda (Hoyer, 1899), Stylonychia jmshdata (Maupas, 

 1889) and Lionotus fasciola (Prowazek, 1909). In Paramecimn 

 caudaiiim the amphinucleus divides twice without differentiatiori 

 and all 4 products divide a third time, 4 of the resulting 8 nuclei 

 become micronuclei and 4 become macronuclei (Calkins and Cull, 

 1907) . Here there is no degeneration but in Paramecimn indrimm, 

 according to Doflein (1916) and in Paramecium bursaria (Hamburger, 

 1904) 3 of the 8 nuclei degenerate. Three divisions of the amphi- 

 nucleus are also characteristic of Criiptochilum nigricans (Maupas, 

 1889), Carchesium yolypinnm (Popoff, 1908), Vorticella monilata 

 and Vorticella nehvlifera (Maupas, 1889) and Ophrydium rersatile 

 (Kaltenbach, 1915). In these, 7 of the 8 resulting nuclei form 

 macronuclei while the eighth forms the micronucleus. All 7 fuse 

 to form 1 macro nucleus in Cryptochihm (Maupas) but in the others 

 each forms a macronucleus the 7 being separated by successive cell 

 divisions until finally each cell has 1 (PopofY, Maupas, Kaltenbach). 

 In Didiniuni nasuUnn (Prandtl, 1906), Paramecium bvrsaria (Ham- 

 burger, 1904) Glaucoma scintillans, Lencophrys pahda, Spirostomwn 

 teres and Stylonychia pustulata (Maupas, 1889) differentiation occurs 

 with the second division; 2 of the 4 nuclei become macronuclei and 

 2 micronuclei while none degenerates. A very exceptional history 

 occurs in Bursaria truncatella according to Prowazek (1899). Here 

 no differentiation occurs until 16 nuclei are formed; 2 to 5 of these 

 become macronuclei; 3 or more become micronuclei and the remain- 

 der degenerate. 



In Sporozoa metagamic activities take quite a different form. 

 The majority of gregarines become gamonts which form many 

 gametes (in Ophryocystis only one), which copulate within the 

 sporocyst (Fig. 180, p. 425). The amphinucleus of each zygote 

 divides, usually three times, to form eight products each of which 

 becomes the nucleus of a sporozoite. In Diplocystis schneideri 

 the first of these divisions results in the reduction in number of 

 chromosomes to one-half (Jameson, 1923; see p. 533). In the 

 Coccidia the number of metagamic divisions is still further increased. 

 Here the zygote as well as the amphinucleus divides to form from 

 two to many sporozoite-forming centers— the sporoblasts— each 

 of which becomes enclosed in a special sporoblast capsule where it 

 divides, usually only once, to form sporozoites (see p. 419). In 



