376 University of California Publications in Zoology [Vol. 18 



the absorption of the old cirri their fibers disappear, apparently being 

 absorbed in the cytoplasm by dedifferentiation. 



At first it was thought that the new fibers formed by a splitting 

 of the old fibers, but it was soon seen that such an hypothesis was of 

 no value for the following reasons : first, the new cirri do not form 

 along the lines of the old fibers. Those for the anterior cell are as far 

 apart as the old cirri of the posterior daughter, while the original 

 fibers in that part of the cell were much converged. Thus the cirri 

 are not formed in a position where it would be possible for the new 

 fibers to form by a splitting of the old ones. In the second place, the 

 new fibers are usually nearer the pellicle than the old ones. As the 

 cirri become heavier they sink deeper into the ectoplasm and carry the 

 fibers with them. Then, too, no indication has been seen that would 

 lead to the conclusion that any splitting of the old fibers occurs. Such 

 evidence leads one to no other conclusion than that the fibers arise 

 independently apart from the original fibers. 



As was stated in connection with the formation of the new cyto- 

 stome, there is a line to which the granules of the new membranelles 

 connect. This inner line becomes the fiber extending along the left 

 and anterior sides of the cytostomal field. This fiber, too, is then 

 differentiated out of the ectoplasm in the same way as the other fibers 

 of the associated neuromotor apparatus. By the growth of the series 

 of membranelles it is carried forward and around the anterior end of 

 the cytostomal field. Such growth brings it around in the position of 

 the new motorium. From this fiber the sensory apparatus of the 

 anterior lip grows out, but its growth has not been seen before division 

 is complete. 



The formation of the new motorium is the most difficult to make 

 out. The original motorium remains in the anterior animal and the 

 new fibers grow forward to connect with it. Due to the unusually large 

 amounts of food in Euplotes at the time of division, few cases have 

 been clearly seen in which the formation of the new motorium could 

 be studied. Plate 16, figure 21. shows a case in which in the anterior 

 end of the posterior daughter Euplotes a number of bright red granules 

 could be distinctly seen. These lay at the point where the fibers are 

 drawn together when the animals w^ere cut apart. As to the origin 

 of these granules which are the new motorium there are three possi- 

 bilities : One is that they form where the fibers are drawn together by 

 the constriction of the animal ; another is that the membranelles come 

 in contact with the fibers from the anal cirri and the fibers form at the 



