SEX IN PROTOZOA 159 



may even fuse wirli rlic fciir.ilc nucleus. Sometimes chains of gametes 

 result from incomplete fusion of gvnandromorpiis. A female gamete 

 may be found at the anterior end of such a chain and a male gamete 

 at the posterior end. Rarelv^ autogamy niav take place within a cyst. 



Eiicovwiiyvipha shows some morphological similarities to 7V/- 

 chovyuiphit, although placed in a separate family 1)V Cleveland. The 

 sexual cycle of E. i/nla (Cleveland, 1950d) is similar to that of 

 Tricboiiyvipha in many respects, but there are characteristic differ- 

 ences. 



The asexual animal (Fig. J, 1) is haploid wnth about fifty chro- 

 mosomes. It begins its sexual activities about 4 or 5 days before the 

 host molts by becoming a gametocyte without obvious morphological 

 change. This divides into a male and a female gamete by a single 

 nuclear and cytoplasmic division. As a rule, the male gamete is con- 

 siderably smaller than the female and its cytoplasm stains more darkly 

 because it contains many stainable granules. There is no special fertil- 

 ization area as in Trichonyuipha, males becoming attached to and 

 entering almost any part of the female gamete. At the point of con- 

 tact, the cytoplasm of the female begins to soften to permit the en- 

 trance of the male (2). However, the body of the male gamete does 

 not enter completely into that of the female. When half or more of 

 the male gamete has entered, its anterior end turns posteriorly and 

 the male organelles begin to degenerate. A4ost of the flagella and asso- 

 ciated structures are dissolved, but the rostrum, sometimes with the 

 axostyles and rostral flagella, projects posteriorly (3) and is pinched 

 off and discarded. 



The freed male pronucleus moves to and fuses with that of the 

 female, thus producing a zygote (4). Further development is sus- 

 pended for about 4 days, then chromosome duplication occurs, but 

 not the centromeres. As the achromatic figure is developed by the 

 centrioles (those of the female gamete), pairing of chromosomes oc- 

 curs and tetrads are formed and divided (5), the daughter dyads going 

 to opposite poles. Cytoplasmic division completes the first meiotic 

 division. The second meiotic division, of the usual sort, produces hap- 

 loid vegetative individuals, which multiply by asexual mitoses as do 

 other similar flagellates. 



Sometimes two male gametes will fuse with the same female. 

 There is no encystment at any part of the cycle. 



Leptospkonympha, the next hypermastigote to be considered by 



