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GENERAL EMBRYOLOGY 



G 



FIG. 72. Early stages in the maturation of the Dipnoan, Lepidosiren paradoxa. 

 After Agar. X 933. A. Polar view 'of equatorial plate of late spermatogonium, 

 showing size and form differentiation and pairing of chromosomes. B. Spireme 

 stage (leptonema) of primary spermatocyte. Only a few of the threads are 

 shown. C. Nearly polar view, showing beginning of longitudinal fusion of 

 chromatin threads; beginning of synapsis (zygonema). D. Nearly polar view 

 of "bouquet stage" (pachynema). The threads are fused and condensed. 

 E. Polar view showing beginning of contraction (synizesis) and splitting of the 

 chromosomes (diplonema). Most of the thickened threads have split apart 

 except terminally, where they remain fused, forming rings. In some, the 



