1923] HaU: Binary Fission of Menoidium incun'uin 461 



extending gradually to complete fusion. Two " reduction divisions" 

 occur, producing in each conjugant a "reduced" nucleus and two 

 "reduction" nuclei, the latter comparable with the polar bodies of 

 oogenesis ; the ' ' reduced ' ' nuclei unite to form a ' ' zygote nucleus. ' ' 

 The flagellum of one flagellate is drawn in, while that of the other 

 persists, serving to keep the precocious pair in locomotion. After 

 fusion, this 'zygote' animal is said to have its choice of remaining 

 a single large flagellate which will later divide, or of encysting. Wliile 

 it is probable that Dobell really observed an apparent fusion, the 

 question remains as to whether or not such behavior is to be interpreted 

 as isogamy. Occurring as it does under such conditions that "Even 

 in my most healthy cultures a number of monads always underwent 

 degenerative changes and died" (Dobell, 1908, p. 102), and that "one 

 can often observe degenerating monads side by side with perfectly 

 healthy individuals in active division or conjugation" (Dobell, 1908, 

 p. 103), the interpretation of this process as conjugation must remain 

 subject to criticism. Berliner's (1909) description of isogamy in 

 Copromonas major is quite similar, so that to both of these reports 

 Dobell 's criticism (Dobell and O'Connor, 1921) of Woodcock's de- 

 scription of conjugation in CcrcoinuDas might appropriately be 

 applied : 



. . . believes he has observed conjugation in ... I have not done so, and 

 coni=ider — from the account published — that there is little or no evidence that 

 conjugation occurs. The phenomenon observed . . . api^ears rather to lie an 

 abortive or regressive fission. . . . 



Weisse (1856) describes small individuals of Euglena. or "Sperm- 

 atozoids, " which penetrate the cj'Sts of larger individuals of Euglena, 

 thus effecting fertilization. Haase (1910) describes the formation of 

 gametes in Euglena sanguinea by an intrakaryosomal mitosis, and 

 the union of free gametes to form a zygote ; the proof offered by her 

 figures is entirely inadequate, however, and her interpretation is 

 evidently at fault. With such little evidence for sexual behavior, 

 the occurrence of sexual reproduction in the euglenoids must, for the 

 present at least, remain doubtful. Other points of controversy have 

 been the nature of the outer chromatin and its behavior in division, 

 and the nature of the endosome — its function in division, and whether 

 or not it contains a centriole. 



