480 JOHNSON. [Vol. VIII. 



structure so obscure as to escape detection. In S. cceriileus 

 the structure of the ectoplasm is further masked by the 

 abundant pigment, which it is impossible to remove. Not- 

 withstanding these observational difficulties, Biitschli ('89, p. 

 1298, Fig. 14 d) has figured an alveolar structure for the ecto- 

 plasm of S. ccznileus ; but after repeated efforts, I am still 

 unable to make it out. 



The functions of the animal that have reference to the out- 

 side world — sensation, locomotion, contraction — are performed 

 by the ectoplasm and its derivatives, cilia and myonemes ; those 

 that concern the internal economy of the organism — digestion, 

 assimilation, excretion, and secretion — are subserved by the 

 endoplasm. An important exception is presented by the mem- 

 branellae, whose two functions, capture of food and locomo- 

 tion, certainly have reference to the outside world; and yet, 

 contrary to the general opinion, I have found them to be deriv- 

 atives of the endoplasm. 



2. Ectoplas7nic Structures. 



Pellicida} — In common with the Ciliata generally, the 

 Stentors possess an external limiting membrane which corre- 

 sponds morphologically to the cell-membrane of pluricellular 

 animals. While the pellicula confines the soft cytoplasm and 

 helps to give the cytosome a definite form, it is at the same 

 time wonderfully elastic and flexible, and admits of the striking 

 mobility characteristic of all species of the genus. In the 

 living animal the pellicula is not very apparent as a distinct 

 structure, although brought into evidence by certain folds 

 or wrinkles which appear most frequently at the anterior 

 end, and by numerous minute transverse crenulations along 

 the blue stripes, often seen when the animal is contracted 

 (Fig. 28). 



After treatment with .25 per cent, osmic acid the pellicula 

 becomes raised from the ectoplasm along the granular stripes, 

 but remains adherent at the clear stripes (Fig. 5,//.). It is 

 then seen to be a thin, structureless membrane. 



1 This term was first used by Biitschli to replace the older and inappropriate 

 name cuticula. 



