ILLUSTRATIONS. 



EXPLANATION OF PLATES. 



The niag-nifications given are those wliicli the figures possessed before reduction. 

 Plat«s IV to VIII have been reduced one-half, 

 so, solution plane, 

 re, reconstruction plane. 

 P, new peristome. 



O, definitive opening of the invaginated new peristome. 

 S. O., rudiment of new suboral membranellae. 

 , az, old adoral zone. 

 AZ, new adoral zone, 

 ph. pharynx (old), 

 sni, suboral membranelUie (old). 



Plate IV. 



Pigs. 1, 2, 3, and 4. Successive stages in the reconstruction of the meganucleus, 

 and of the invagination of the new peristome. X 800. Camera lucida. 

 Fig. 5. Micronuclear spindle of figure 4. X 1,600. 



6. Posterior extremity of meganucleus of figure 3. The chromatin reticulum 



on the anterior side of the solution plane ends very abruptly and 

 evenly. On the posterior side of the reconstruction plane the chro- 

 matin libers reappear; the chromatin is nodular in the posterior 

 part of the nucleus. X 1,600. Camera lucida. 



7. Transverse section of a stage corresponding to figure 4. The invagina- 



tion of the new peristome (P) is seen below the old adoral zone. 

 The new adoral membranellfe stand inside the invagination. X 600. 

 Camera lucida. 



Plate V. 



Fig. 8. The invagination of the new peristome is completely closed. X 800. 



Camera lucida. 

 9. Micronucleus of figure 8. Spindle threads connecting the poles could 



not be seen. X 1,600. 

 10. The peristomial invagination is reopening at 0. At S. 0. appears the 



rudiment of the new snboral gi'oup of membranellse. X 800. Camera 



lucida. 

 11 and 12. Solution and reconstruction plane.s. Both these nuclei show a 

 :■ reticulum of extremely fine fibers in the reconstruction plane. These 



are thickest on the side away from the solution plane; little masses 



of chromatin can be seen forming at the nodes. X 1,600. Camera 



lucida. 



13. The opening of the new peristome is enlarging. The micronucleus has 



divided, the two new micronuclei still showing the points at which the 

 nuclear membrane was drawn out as the poles moved apart. X 800. 

 Camera lucida. 



14. The new peristome now has a large opening. The two micronuclei are. 



entirely reconstructed, and have assumed their final positions. The 

 reconstruction bands of the meganucleus are approaching each other, 

 while the meganucleus as a whole is condensing and . shortening. 

 X 800. Camera lucida. 



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