1918] Yocum: The Neuromotor Apparatus of Euplotes Patella 375 



difference is that E. patelli has the prominent anterior lip, while in 

 E. worcesteri this is absent and the right anterior field overhangs the 

 adoral field much more. Such a depression is heartily in accord with 

 the idea that the new peristome forms quite independently of the old 

 peristome. This is more significant than it may appear at first sight. 

 In our consideration of the formation of the new neuromotor appa- 

 ratus it will be pointed out that this structure forms from the ectoplasm. 

 It was also seen that new cirri are of ectoplasmic origin. In the 

 description of the formation of the new cytostome a heavy staining 

 line was mentioned as appearing very soon after the depression has 

 sunken into the ectoplasm. This is undoubtedly differentiated out of 

 the ectoplasm. Very soon rows of granules form, which are the basal 

 granules of the new membranelles. These, too, are ectoplasmic in their 

 origin, for they form on the under side of the pellicle. It is thus 

 quite evident that the new membranelles form not from the old mem- 

 branelles but independently in an area quite set off from the old 

 cytostome. This origin of the new cytostome in E. patella bears out 

 the contention of Griffin (1910) that the new cytostome develops quite 

 independently of the old cytostome and that the whole structure — lip, 

 cytostomal field, membranelles and basal granules — develops de novo 

 and are ectoplasmic in their origin. 



Formation of the Neuromotor Apparatus 



We now come to a description of the formation of the neuromotor 

 apparatus at the time of binary fission, which must be given in its 

 relation to the other parts which have just been described. Very soon 

 after the formation of the new anal cirri for both daughter organisms, 

 there can be seen extending forward from them fine but distinct 

 fibrils having the same staining reactions as the old fibrils (pi. 16, 

 figs. 18-21). In appearance they are the same, except that in the early 

 stages they are much finer and nearer the surface than the old fibers. 

 Usually the fibers from the anal cirri of the anterior daughter are to 

 be seen before those from the posterior cirri. Early in their develop- 

 ment the fibers are quite distinct near the cirri, but as they extend 

 anteriorly toward the motorium they become much finer and are lost 

 to view in the cytoplasm. This leads one to the conclusion that the 

 fibers are ectoplasmic, rather than endoplasmic as Griffin (1910) 

 stated, and that they grow out from the new cirri toward the anterior 

 end. The old fibers persist until the new fibers are formed, but with 



