20 DESCRIPTION OF PLATES. 



[The figures of plates i-vi were all drawn with Zeiss oil-immersion 2 mm., 

 cc. 12, and have been reduced one-third ; those of plate vii with oc. 8, not reduced.] 



Plate I. 



Termopsis angusiicollis. 



Figs. 1-3. Resting nuclei of spermatogonia, showing division of nucleolus. 

 4. Equatorial plate of spermatogonial mitosis, 52 chromosomes. 

 5-6. Young spermatocytes, showing division of nucleolus. 

 7. First maturation spindle, and two nuclei (6 and 8) in same cyst. 

 8-10. Skein-stage — so-called synapsis-stage. 

 11-14. Bouquet-stage, showing two nucleoli, centrosome (c) in fig. 11, and 



loops made up of fine, then coarser granules. 

 15-17. Stage following preceding; loops straightened out and extending in 

 various directions through nucleus. 



18. a, Chromosomes much shortened and longitudinally split; b, chromo- 



somes contracted to form diamond-shaped figures. 



19. Stage between i8a and i8b. 



20. Stage between 19 and 18b. 



21. Stage similar to i8a, one chromosome in double diamond form. 



22. First maturation spindle in metaphase, chromosomes in single and 



double diamond shapes. 



23. Chromosome in single diamond or tetrad form, as they usually come 



into the spindle. 



24. Double diamond-form assumed before metakinesis. 



25. The 26 chromosomes of an early metaphase. 



26. First maturation spindle in metakinesis. 



27. Equatorial plate of first maturation spindle in metakinesis. 



28. Another spindle, showing three granules which are probably remains 



of nucleoli. 



29. Anaphase of first maturation mitosis, one centrosome divided. 



30. Late anaphase. 



31-32. Telophase, exceptional cases of division of the cell. 



33-36. Partial rest stage between first and second maturation divisions, two 



nucleoli present. Chromosomes in fig. 36 in form of double diamonds 



ready for metakinesis. 

 37-38. Second maturation spindle in metaphase. 



39. Equatorial plate of second maturation spindle, 26 chromosomes. 



40. Same in anaphase. 



41. Four spermatid nuclei in one cell, each nucleus containing one nucleolus. 



42. A later stage, showing elongation of nuclei, centrosome and sphere at 



posterior end. 

 43-45. Later stages in the development of the spermatozoa, nucleolus grows 

 gradually smaller. 



