A Cytological Study of the Semi-parasitic Copepod, Hersilia apodiforniis etc. 445 



Fig. 22, Cell showing condensation and thickening of strepsistene tlu'cads to 

 form di-tetrads. 



Fig. 23. Types of di-tetrads found in early prophase of first spermatocyte. 



Figs. 24a and 2ib. Two sections of a Single cell. Early prophase of first spermato- 

 cyte division. Ring di-tetrad prevailing form. 



Fig. 25. Tjijes of di-tetrads in late prophase or in metaphase of first spermatocytes. 



Figs. 26a and 26b. Two sections of a cell in late prophase. 



Fig. 27. Metaphase plate of first spermatocyte, prevailing type with 13 chromosomes. 



Fig. 28. Stage corresponding to Fig. 27, but of less frequeut occiirrence with 

 12 chromosomes. 



Plate VI. 

 Figs. 29 — 43. Spermatocytes and Spermatids. * 



Fig. 29. Lateral view metaphase, first spermatocyte. 



Fig. 30. Lateral view early anaphase. 



Fig. 31. Lateral view late anaphase, showing the lagging heterochromosomes, h. h. 



Fig. 22. Lateral view, stage slightly later than that of Fig. 31. Passing of the 

 heterochromosomes to the sister plates. 



Figs. 33a and 33b. Two sections of a Single second spermatocyte in the intcr- 

 kinetic phase. 



Fig. 34. Types of chromosomes from a single nucleus of the interkinetic stage. 



Fig. 35. Metaphase equatorial plate, second spermatocyte. Eleven chromosomes 

 with "Querkerbe", one single. 



Fig. 36. Metaphase second spermatocyte, lateral view, 



Fig. 37. Metaphase plates of two sister spermatocytes , with spindles lying 

 parallel in the undivided cytoplasmic mass of the primary spermatocyte. 



Fig. 38. One of the exceptional cases in which a lagging chromosome of the 

 first spermatocyte is included between the sister second spermatocytes, here seen iu 

 metaphase. 



Fig. 39. Anaphase, two sister second spermatocytes showing lagging hetero- 

 chromosome. 



Fig. 40. Late anaphase of second spermatocyte. 



Fig. 41. Spermatid showing heterochromosome lying separate from the autosomes. 



Figs. 42 and 43. Spermatids showing the inclusion of the heterochromosome 

 into the nucleus. 



Fig. 44. Oögonia metaphase equatorial plate, showing 24 chromosomes, 



Fig. 45. Oöcyte, leptotene stage. 



Fig. 46. Oöcyte, showing conjugation of chromosomes. 



Fig. 47. Oöcyte in bouquet stage. 



Fig. 48. Form of tetrad j iist previous to the f ormation of the primary oöcyte spindle. 



Fig. 49. Metaphase equatorial plate of primary oöcyte. 



Fig. 50. Same as Fig. 49, in lateral view. 



Fig. 51. Chromosome of primary oöcyte spindle stained with crystal-violet- 

 alizarin after Flemming fixation. 



Fig. 52. Metaphase equatorial plate of tlind cleavage of egg. 



Fig. 53. Section of blastula passing tlu-ough primordial germ cells. x 520. 



Fig. 54. Nucleus of primordial germ cells from blastula, such as shown in Fig. 53. 



