FERTILIZATION 627 



maturation spindle is formed at right angles to the prophase crescent by 

 the migration of the division center from the apex of the crescent to the 

 middle of the crescent, and by the pushing out of the other pole across 

 the crescent. Earlier workers believed the spindle was formed by a 

 shortening of the crescent. Dehorne finds no chromosomes at all, but, 

 instead, a simple convoluted thread. 



In a wide variety of other ciliates, the prophase develops a "cande- 

 labra" (Collin, 1909) or "parachute" (Calkins, 1919) stage. It is 

 noteworthy that the parachute prophase occurs in most of the ciliates in 

 which reasonably complete chromosome studies have been made and 

 reduction definitely located. Kidderia [Concho phth'nius) jjiytili may be 

 an exception to this, but Kidder (1933a) admits he might have missed 

 finding it. Tannreuther (1926) describes a simple type of chromosome 

 formation in Prorodon griseus, in which chromosomes arise directly out 

 of a central chromatin mass upon the equator of the spindle. 



In Euplotes patella a typical parachute is formed, which is seen as 

 a stage in the transformation of resting chromatin into the chromosomes 

 of the metaphase spindle. The events transpire synchronously in both 

 nuclei produced by the preliminary, or pre-maturation division of the 

 micronucleus occurring in this species. Each nucleus swells to several 

 times its original size, as the faintly granular chromatin becomes more 

 basophilic, and is arranged in a reticulum filling the nuclear space (Fig. 

 148) . The reticulum condenses in the center and becomes polarized, with 

 most of the chromatin at one pole. Further condensation forms a dense 

 club-like structure, which presently loosens up and is transformed into 

 a parachute, with most of the chromatin forming the "cloth" at one pole, 

 the spindle fibers forming the "rope," and an endosome at the other pole 

 forming the "weight." The chromatin then forms thirty-two discrete 

 chromatin granules, the chromomeres, which soon migrate to the equa- 

 torial plate in groups of four. These eight groups of four chromomeres 

 apparently correspond to the eight diploid chromosomes found in other 

 stages of the life cycle. In the anaphase of this division, sixteen chromo- 

 meres pass to each pole, and one may frequently observe them associated 

 in pairs as loosely connected dumb-bells. The sixteen chromomeres, or 

 eight dumb-bells, which pass to each pole represent the eight diploid 

 chromosomes and identify this as an equational division. 



In Pleurotricha lanceolata, Manwell (1928) found chromomeres that 



