II 



MEIOSIS IN ASCARIS 



51 



By the later stage shown in Fig. 20, C, synizesis has completely dis- 

 appeared, and all the chromatin is in the form of a long, doubly spUt 

 thread (only one split is visible in the plane of the figure). As there are 

 really two bivalent chromosomes present, these must be joined tempor- 



FiG. 20. 



Meiosis in Ascaris megalocephala bivalens. (A-M, after Brauer, A .m.A ., 1893 ; N-P, after O. Hertwig, A .m.A., 

 1890.) A, B, synizesis and syndesis ; C, D, E, formation of the definitive bivalents. In E the left-hand bivalent 

 is seen in side view and therefore only two of the constituents are visible ; the right-hand bivalent is seen in 

 end view, and therefore its quadruple constitution is revealed. F, metaphase I. ; G, H, anaphase I. ; I, 

 preparation for second division ; J, metaphase 11. ; K, anaphase II. ; L-M and N-P, condensation of the 

 definitive bivalents in nuclei in which the four constituents of each are well separated. 



arily end to end to form an " unsegmented spireme " as described on p. 9. 

 Later (D) this dissociates into its two components. Each of these is a 

 bivalent chromosome, longitudinally di\dded into four owing to the fact 

 that each constituent univalent is, as described above, itself longitudinally 

 divided. The quadruple nature of each bivalent chromosome is well 



