EEPEODUCTIVE ELEMENTS IN APUS AND BRANCHIPUS. 283 



PLATE 16. 



Fig. 24. — Portion of epithelium of the female gland of Apus. 



Fig. 25. — Single cell with nucleus in partial division. 



Fig. 26.— Ditto. 



Fig. 27. — Irregular formation of tetrad group. 



Fig. 28. — Element with four nuclei. 



Fig. 29. — Tetrad formed from a single cell. 



Fig. 30. — Three nuclei of a tetrad, showing micronucleoli (a). 



Fig. 31. — Two tetrad groups in relation to surrounding cells. 



Fig. 32. — Cell with dividing nucleus. 



Fig. 33. — Portion of nuclei of tetrad, showing the minute subdivision of 

 the nuclei. 



Figs. 34 and 35. — Method of division occurring in same nucleoli. 



Figs. 36 — 41. — Stages of division. 



Fig. 42. — Tetrad group, the upper cell being the future six " Nebenkern." 

 a, a, a. Nuclei which have spread over the circumference of the group. 



Fig. 43. — Group of cells from the spermatic gland of Branchipus. 



Fig. 44. — Ditto, ditto, from the female gland of Branchipus, showing the 

 relation of the akinetically dividing elements to the formation of slime. 



All the preparations, except where otherwise stated, were fixed in Fleni- 

 ming's fluid and stained with gentian violet. 



