388 The Ohio Naturalist. [Vol. IX, No. 1, 



EXPLANATION OF PLATE XXI. 



The drawings were made with a No. 12 compensating ocular 

 and a 1-12 oil immersion objective, the original magnification 

 being 2250 except figure 21 for which a No. 18 compensating 

 ocular was used. The plate is reduced one-third in reproduction. 



Fig. 1. Two cells from a very young antheridium, showing cen- 

 trosomes on opposite sides of the nucleus. 



Figs. 2-3. Mother star stage from a very young antheridium, with 

 centrosomes at the poles. 



Fig. 4. Daughter star stage showing elongated centrosomes, from 

 very j^oung antheridium. 



Fig. 5. Great grandmother cells, or earlier, showing centrosomes on 

 opposite sides of the dividing nuclei. 



Figs. 6-9. Great grandmother cells, or earlier, with centrosomes at 

 the poles of the spindle. 



Figs. 10-15. A series of great grandmother cells, showing the 

 appearance of the centrosomes and in some cases dark-staining asters. 



Figs. 16-20. Grandmother cells in various stages of division, 

 showing centrosomes at the poles. 



Fig. 21. A grandmother cell with prominent centrosomes. 



Figs. 22-32. Spermatozoid mother cells in process of division, 

 showing the same kind of centrosomes as are in the earlier divisions. 

 Fig. 25 shows eight distinct chromosomes. 



Figs. 33-40. Spermatids or incipient and young spermatozoids, 

 showing the increase in size of the centrosome (blepharoplast) as it is 

 being transformed into an elongated cilia-producing oi-gan. 



