PHENOMENA ACCOMPANYING FERTILIZATION 315 



living cell. It is small at first but grows in size from day to day 

 while nucleic acid is formed and deposited in continually growing 

 chromomeres (Calkins, 1930; see p. 84), until finally the placenta 

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

 compact homogeneous ellipsoidal nucleus, invisible in the living 

 cell, and now stains intensely with chromatin dyes (Fig. 160, 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 8 macronuclei 

 prior to cell division in vegetative life (see p. 220). 



An essentially similar history of the amphinucleus occurs in 

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

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

 caudatum the amphinucleus divides twice without differentiation 

 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 Paramecium putrinum 

 according to Doflein (1916) and in Paramecium bursaria (Ham- 

 burger, 1904) 3 of the 8 nuclei degenerate. Three divisions of the 

 amphinucleus are also characteristic of Cryptochilum nigricans 

 (Maupas, 1889), Carchesium polypinum (Popoff, 1908), Vorticella 

 monilata and Vorticella nebulifera (Maupas, 1889) and Ophrydium 

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

 form macronuclei while the eighth forms the micronucleus. All 7 

 fuse to form 1 maeronucleus in Cryptochilum (Maupas) but in the 

 others each forms a maeronucleus the 7 being separated by succes- 

 sive cell divisions until finally each cell has 1 (Popoff, Maupas, 

 Kaltenbach). 



In Didinium nasutum (Prandtl, 1906), Paramecium bursaria 

 (Hamburger, 1904), Glaucoma scintillans, Leucophrys patula, Spiro- 

 stomum teres and Stylonychia pustulata (Maupas, 1889) differentia- 

 tion occurs with the second division; 2 of the 4 nuclei become macro- 

 nuclei and 2 micronuclei while none degenerates. A very exeeptional 

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

 Here no differentiation occurs until 10 nuclei are formed; 2 to 5 of 

 these become macronuclei; 3 or more become micronuclei and the 

 remainder degenerate. This history, however, is not confirmed by 

 Poljansky (1928) in a more critical examination of this phase of 

 Bursaria. 



In Sporozoa metagamic activities take quite a different form. 

 The majority of gregarines become gamonts which form many 

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

 gametocyst (Fig. 120, p. 231). 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 



