32 Vniversity of California Publications in Zoology [Vol. 20 



some (fig. B, 1). This is followed by a division of the centrosome. 

 As the two new centrosomes move apart a darkly staining line or bar 

 is drawn out between them, the paradesmose (fig. A, 5, parad. ; fig. B). 



The rhizoplasts connecting the centrosomes with the blepharo- 

 plasts gradually elongate with the paradesmose also increasing in both 

 length and thickness. The latter structure with its connected centro- 

 somes moves down until it comes to rest upon the nuclear membrane 

 (fig. B). As a result of this the centrosome-rhizoplasts come to have 

 the same length as the nuclear rhizoplasts. All four of these rhizo- 

 plasts are exceedingly delicate, particularly the nuclear ones and the 

 latter especially long escaped our notice. Since the two are rather close 

 together (fig. B, 5) their distinctiveness may be easily overlooked. 

 The centrosomes (fig. A, 5, cetit.) are minute knobs on the ends of the 

 paradesmose, which is a stout, heavj', sometimes granular, deeply 

 staining bar. They are not always visible as expansions of the bar and 

 are never seen detached from it. 



In the meantime the new undulating membrane and parabasal 

 body have reached sizes equal to the ancestral ones (pi. 3, fig. 11; 

 fig. B, 2-6). The parabasal body first appears as a slender dark 

 thread growing posteriorly subparallel to the old parabasal in the 

 peripheral cytoplasm (pi. 3, fig. 5). "With the beginning of the 

 formation of the paradesmose (fig. B, 2) the new flagella have all 

 formed by outgrowth from the daughter blepharoplasts, two anterior 

 ones and a posteriorly directed one as a marginal filament from the 

 blepharoplast attached to the new parabasal, and only one anterior 

 one from that attached to the old parabasal. At first (fig. B, 2) the 

 new undulating membrane is very narrow but it soon attains full 

 structural size and functional efficiencj' (pi. 3, fig. 11). With the 

 completion of these structures by growth the diiplication of the neuro- 

 motor system is accomplished. 



Up to this time the changes visible within the nuclear membrane 

 have been very slight. The chromatin granules or chromomeres grow 

 larger and darker, and evidences of polarization appear in the linear 

 grouping of the granules (fig. B, 6; pi. 3, figs. 6-10) which cul- 

 minates in the emergence of linear V-shaped chromosomes. During 

 this process a deeply staining cone-shaped extension of the central 

 chromatin mass projects anteriorly until it comes in contact with 

 the paradesmose (fig. B, 6; pi. 3, figs. 6-8). As this disappears the 

 V-shaped chromosomes become more evident in the central mass, and 



