168 PROCEEDINGS OF THE ACADEMY OF [1895. 



be very faintly striated in optic section the strire extending through it, 

 and closely approximated to one another. The cuticle is smooth and 

 entirely without cilia in this condition, so that a tannic acid solution 

 enables one to completely remove the cilia and also to separate the 

 cuticle from the underlying plasma. The tannic acid acts, in short, as 

 a sort of "depilatory," removing, apparently, every vestage of cilia 

 from the creature. The "threads" thus removed are very long 

 and of nearly the same thickness throughout. They are not much 

 shorter than the short diameter of the body of the creature, but do 

 not taper as do the cilia. 



This singular behavior of tannic acid in removing all trace of the 

 presence of cilia from the body of Paramcecium has led me to doubt 

 the non- ciliary nature of the threads thrown oft' by the body of this 

 infusorian. If these threads are not cilia why should there be no 

 trace of cilia left on the cuticle after the prolonged action of a 

 solution of tannic acid ? These threads form a dense mat of tangled 

 fibres in the midst of which lie the shriveled remains of its sarcode 

 covered by the cuticle that is now lifted up and everywhere freed 

 from contact with the ectosarc if the creature is subjected to prolonged 

 treatment with tannic acid solution. On Euplotes, Stylonchia and 

 Halteria tannic acid has no such action, proving that these organisms 

 in some way differ very widely in their reaction toward that reagent 

 as compared with the slipper-animalcule. This singular power of 

 tannic acid gives rise to grave suspicions as to the truth of the state- 

 ment that the "threads" developed by tannic acid on the surface of 

 Paramcecium are something different from the cilia. In order to test 

 this suspicion it was necessary to resort to sections of the infusorian 

 in question to see if there really was any ground for the very positive 

 statement of E. R. Lankester and T. J. Parker as to the existence 

 of a fundamental difference between these so-called " nettle- threads" 

 and the cilia of Paramcecium. 



2. By the aid of a method of entrapping, killing and embedding 

 infusoria and other very small objects in paraffine invented by me 

 and fully described in the American Naturalist, XXIX, 1895, pp. 

 194-198, it has been possible to obtain serial sections of Paramcecium, 

 in quantity, of a thickness not exceeding 2.5 mikrons, , () ' lino inch. 

 These sections so fully reveal the true structure of the ecto- 

 sarc that nothing further is needed to show how completely this 

 agrees with the view that the "nettle-threads" are nothing but 



