SEX IN PROTOZOA 161 



Clevchind (1 95 la), is placed in the Spirotrichonymphidae. It has a 

 rosrral area at the anterior end, and two long spiral flagellar bands 

 reaching nearly to the posterior end of the cell. L. uoachiila (Fig. K, 

 1) has an axostyle, but L. eupora lacks this organelle. 



A vegetative individual of L. wachula becomes a gametocyte by 

 loss of the axostyle and the long flagellar bands and a rearrangement 

 of the flagella in the rostral region (2). Also, the cytoplasm becomes 

 denser, becoming filled with many small dark granules. Thus the 

 gametocyte presents a decidedly different appearance from that of 

 vegetative cells. 



Gametogenesis is initiated by duplication of the ten chromo- 

 somes, each of which produces sister chromatids. This occurs between 

 the sixth and fifth days before the host molts. Some of the chromatids 

 are darker than others, but the contrast is not so marked as in Tricho- 

 iiyvipba. However, as in the latter genus, the chromosomes become 

 arranged into tw^o groups which separate from each other in the 

 ensuing gametogenic mitosis. That is, a male set separates from a 

 female set (3). Cytoplasmic division follows very quickly and may 

 take place before nuclear separation is complete, and even sometimes 

 so early that an anucleate cell is produced. An anucleate male was 

 seen to attach itself to a female gamete. 



The organization of the gametes is like that of the gametocytes 

 except that the female has more cytoplasmic granules which tend to 

 congregate near the posterior end of the cell, and this area alone is 

 attractive to the male gamete, as in Trichoiiympha. By the time a 

 male gamete has pushed half way into the cytoplasm of the female 

 (4), the two cytoplasms begin to fuse and the male gamete progresses 

 no farther. The cytoplasmic organelles of the male gradually disin- 

 tegrate while the male pronucleus migrates to and fuses w^ith that of 

 the female. During fusion of the gamete nuclei, the chromosomes are 

 tightly coiled (5, 6) and remain so during the ensuing meiotic divi- 

 sion. Thus the chromosomes are not duplicated and pairing is slight. 

 The undivided homologues are segregated on the spindle that is 



Fig. J. EiicoDwnyiupha hnla, from Cleveland (1950d). 



1, an agamont seen partially in optical section; 2, stage in union of gametes; 3, 

 rostrum of male gamete has rotated 180 degrees, rostrum of female gamete should 

 extend anteriorly but has been bent in fixation; 4, male pronucleus in contact with 

 female pronucleus, male rostrum has been discarded, axostyles omitted; 5, metaphase 

 of first meiotic division, with about 50 tetrads, organelles other than centrioles, 

 achromatic figure, and nucleus, omitted. 



