1895.] NATURAL SCIENCES OF PHILADELPHIA. 169 



greatly stretched cilia, that are probably exteuded by some physical 

 action exerted upou them by the tannic acid that has both stretched 

 and swollen them. 



The ectosarc of Paramecium is composed entirely of a system of 

 vertical rods of a plasmic substance that stains somewhat more deeply 

 than the endosarc. These rods are cylindrical and densely packed 

 together with but little clear plasma between them. They extend 

 throughout the whole thickness of the ectosarc and compose more 

 than four- fifths of its substance. They are so closely packed together 

 that their arrangement can very readily be made out to correspond 

 to the origins of the cilia from the cuticle. The arrangement of the 

 cilia is quincuncial, that is, in rows in at least two if not in three 

 directions, which correspond with the mode of arrangement or pack- 

 ing together of the rods of denser plasma of the ectosarc just beneath 

 the cuticle. 



The sections show that where the cuticle is intact and where 

 reagents like osmic acid or corrosive sublimate have provoked the 

 discharge of the "nettle- threads " there are no cilia; where, on the 

 other hand, there has been no discharge of "nettle-thread" there 

 are cilia present. Intermediate stages can also be sometimes dis- 

 covered, that is, partially discharged " nettle- threads " may be 

 observed. These facts seem to me to most distinctly prove that the 

 " nettle- threads " and cilia of Paramecium are identical. No one 

 has yet seen these threads discharged except under abnormal con- 

 ditions. Though I have watched these organisms feeding by the 

 hour I have yet to see that they showed the slightest tendency to 

 throw off the "nettle-threads" except when crushed, roughly 

 handled or brought under the influence of reagents. The fact that 

 few other infusorians have such a distinctly roddecl ectosarc, taken 

 together with the fact that other forms are not affected in the same 

 way by tannic acid leads me to conclude in consideration also of 

 the great number of these rods in the ectosarc of Paramecium that 

 they are connected with the cilia individually and are probably only 

 the expression of the same thing as is seen in the rodded or striated 

 ends of many epithelial cells that bear cilia in multicellular animals. 

 At any rate, whatever else can be established by a reinvestigation of 

 this subject by the aid of the methods I have used, one thing is 

 certain, that tannic acid in solutions of almost any strength will 

 finally remove all of the cilia and leave the cuticle smooth especially 

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