CILIATE FIBRILLAR SYSTEMS 211 



Spasmonetn. In the younger branches it is fairly homogeneous, but in 

 the older stems and in the main trunk one may distinctly observe, in 

 its hyaline ground substance, parallel longitudinal fibrils that gradually 

 disappear toward the distal end. Nodal interruptions in these parallel 

 fibrils apparently account for the cross striations cited by earlier workers. 

 Outside these longitudinal fibrils is a single, or composite, spiraling 

 fibril, and centrally placed along the Spasmonem are ovoid discs, each 

 containing a central granule or "nucleus." 



Entz's Spironem and AxonetJi constitute, as noted above, the Proto- 



cir. fib. 

 1. fib. 



Ci/tO, z^li=^^^^^ 



Figure 77. Three components of Spironem of Zoothamnium. (Entz, 1893.) 

 cir. fib. — circular fibril cyto. — cytophanes 1. fib. — longitudinal fibrils 



plasmastrang. This structural duality had been previously overlooked, 

 perhaps because the Spironem is wound closely around the Axonem. 

 Also, the spirals of the former, which are contiguous when the stalk 

 is fully contracted, separate increasingly as the stalk is extended, so that 

 the two fibers may easily appear as one in the completely extended stalk. 



In its finer details, the Spironem (Fig. 77) shows beneath its investing 

 membrane a spirally wound fibril, under which are several longitudinal 

 fibrils. All these fibrils are birefringent and, as noted for those in the 

 Spasmonem, nodes of less refringence give here also the effect of cross 

 striations. Along the axis of the Spironetn are oval bodies [Cytophanes) 

 containing each a central granule [Caryophane). These Cytophanes are 

 connected by a longitudinal fibril (Fig. 75) similar to a string of pearls. 



In the Axonem (Fig. 75) longitudinal fibrils comparable to those in 

 the Spironem also occur, but their course is apparently completely inter- 



