336 GRIFFIN. 



Fifi. 15. The middk' portion of tlie megaiiucleus of figiu'e 14. X 1,200. Camera 

 hicida. 



16. A vertical longitudinal section of the new peristome at a stage corre- 



sponding to figure 10. The invaginated new peristome forms an 

 extensive cavity lying directly dorsad (below in the figure) to the 

 old adoral zone (az). The opening of the invagination to the ex- 

 terior at is just commencing. The new adoral zone is seen at 

 AZ. X 1,000. Camera lucida. 



17. An obliquely transverse section of a stage corresponding to figure 14, 



passing through the new peristome and its opening, and the old adoral 

 zone (az). X 600. Camera lucida. 



Plate VI. 



Fig. 18. Tiie two solution planes of the meganucleus have met. The meganucleus 

 is considerably condensed. X 800. Camera lucida. 



19. Anaphase of micronucleus. 



20. The solution planes have disappeared and the reconstruction planes have 



met. X 800. Camera lucida. 



21. Late anaphase of micronucleus. 



22. The reconstruction planes have disappeared and most of the meganucleus 



has condensed until the chromatin reticulum is not easily visible. 

 X 800. Camera lucida. 



23. At about the same stage as figure 22, but witli a less condensed mega- 



nucleus. The rudiments of the new cirri have been formed. 



24. A transverse section passing through the old peristome, pharynx, adoral 



zone and suboral membranellir, and also through the new peristome 

 and its opening to the exterior. The latter is at the base of a 

 depression of the outer surface, and one of its edges is shown in the 

 figure. X 400. Camera lucida. 



25. The final stage in the condensation of the meganucleus. Two of the 



old anal cirri have disappeared; the new cirri are increasing in size. 



Plate VII. 



Figs. 26 to 29. Elongation and constriction of the body and meganucleus; the 

 new peristome is drawing out from above the old, and a-ssuming its 

 definite position. 



Fig. 30. Anterior daughter individual immediately after division. 



31. Posterior daughter individual immediately after division. 



32. First stage in the development of the new cirri. A, B, C, D, E, depres- 



sions in which the new cirri of the anterior daughter body will 

 develop; a, b, c, d, e, corresponding depressions of the posterior 

 daughter body; 1, 2, 3, 4, 5, 6, 7, frontal cirri; 8, 9, ID, abdominal 

 cirri; I, II, III, TV, V, anal cirri; LI, L2, left marginal cirri; Rl, 

 R2, R3, right marginal cirri. 



Plate VIII. 



Figs. 33 to 36. Successive stages in the development and arrangement of the 

 new cirri, and in the resorption of the old ones. Figures 34, 35, and 

 36 are drawn from the same individual at intervals of about half an 

 hour. 



