182 



THE PROTOZOA 



Cirri, membranelles, and membranes are each striated, and when 

 treated with certain reagents (e.g. gold chloride, Maupas), can be 

 reduced to separate fibres which are similar to cilia. The simplest of 

 these aggregations are the cirri. These bundles of threads are 

 usually pointed, and either curved or straight, forming the Griffeln 

 und Hakcn of Ehrenberg. A simple condition is seen in the tail-like 

 process of Urocentrum, which has a distinctly fibrillar structure and 

 can be readily reduced to a brush of very fine hairs (Fig. 99). 



Although the striated appear- 

 ance and the reduction to the 

 component fibrils make it prob- 

 able that cirri arise by the 

 fusion of cilia, an objection is 



met in the fact that their de- 

 ^__ -n MA 



\ * velopment, after division, shows 

 \-~em no such origin. On the con- 

 }_ o trary, they arise from the ecto- 

 plasm as cirri and not as cilia. 

 This objection, however, seems 

 2 hardly sufficient to counter- 

 \'1)0 C balance the evidence in favor 

 of the concrescence theory, 

 evidence which is strengthened 

 by the position of the cirri 

 along the lines of the cilia- 

 markings. 



The membranelles are flat 

 plates of striated appearance 

 usually in the form of tri- 

 angles, squares, or parallelo- 

 grams. Each membranelle is 

 inserted in a furrow below 



Fig. 98. Schematic hypotrichous ciliate. 



az.adoral zone; c, ventral cirri ; <>z, endoral mem- which IS a basal Stripe of 

 brane; eo, endoral cilia; pm, praoral membrane ; po, thickened protoplasm COntinU- 

 paroral cilia ; /, praeoral alia. ^ with ^ longitudinal dl _ 



iary markings (Heterotrichida). 



Like the cirri, they can be readily reduced to component fila- 

 ments resembling cilia, and there is, therefore, every reason to 

 suppose that the membranelles which form such a characteristic 

 differential for all orders save the Holotrichida, are merely the differ- 

 entiated portions of the ciliary rows. 1 The basal stripes of the 

 membranelles, which are spirally arranged upon the peristome, are in 

 turn inserted, in some cases at least, in a thick fibrous strand which 



1 Johnson ('93) alone regards the membranelles in Stentor as endoplasmic in origin. 



