REPRODUCTION 137 



anaphase the membrane completely disappears, the equatorial 

 plate sphts and each half contracts in the plane of the plate, pro- 

 ducing two daughter-plates. In some specimens a faint spindle 

 formation was noted. At about this time, vacuolated condition 

 of the perinuclear cytoplasm disappears (/). In later phases of 

 anaphase the plates are more widely separated and are slightly 

 less in diameter as compared with earlier stages. There are dis- 

 tinct polar caps of fibrillar material at the poles of the spindle (g), 

 finally each plate transforms itself into a resting nucleus (h). The 

 two investigators added that if the chromatin granules located 

 in the equatorial plate are chromosomes, ''they must be extremely 

 numerous." Liesche (1938) recently estimates the number of these 

 granules which he called chromosomes as between 500 and 600. 



C5rtosomic division 



Binary fission. As in metazoan cells, the binary fission occurs 

 very widely among the Protozoa. It is a division of the body 

 through middle of the extended long axis into two nearly equal 

 daughter individuals (Fig. 49). In Amoeba proteus, Chalkley and 

 Daniel found that there is a definite correlation between the 

 stages of nuclear division and external morphological changes 

 (Fig. 63). During the prophase, the organism is rounded, studded 

 with fine pseudopodia and exhibits under reflected light a clearly 

 defined hyaline area at its center (a), which disappears in the 

 metaphase (b, c). During the anaphase the pseudopodia rapidly 

 become coarser; in the telophase the elongation of body, cleft 

 formation, and return to normal pseudopodia, take place. 



In Testacea, one of the daughter individuals remains, as a rule, 

 within the old test, while the other moves into a newly formed 

 one, as in Arcella, Pyxidicula, Euglypha, etc. According to 

 Doflein, the division plane coincides with the axis of body in 

 Cochliopodium, Pseudodifflugia, etc., and the delicate homo- 

 geneous test also divides into two parts. In the majority of the 

 Mastigophora, the division is longitudinal, as is shown by that 

 of Menoidium incurvum (Fig. 64). In certain dinoflagellates, such 

 as Cefatium, Cochliodinium, etc., the division plane is oblique, 

 while in forms such as Oxyrrhis (Dunkerly; Hall), the fission is 

 transverse. In Strehlomastix strix (Kofoid and Swezy), Lopho- 

 monas striata (Kudo), Spirotrichonympha hispira (Cleveland), 

 etc., the division takes place transversely but the polarity of the 



