Spiral Structure of Muscle. 183 



When the movements have entirely ceased, the two hnes of cilia 

 lie nearly parallel, fig. 36, n, o, and somewhat bent, with the 

 convexity almost always in the same direction as the current 

 their movements had occasioned. 



It remains to be added respecting the cilia n and o, that when 

 their movements have terminated, and the cilia are left in a state 

 of relaxation, they often in a short time entirely disappear. Pro- 

 bably most of them break off at their roots, as indeed may con- 

 stantly happen during life, when the old ones become replaced 

 by new, the former going off when worn out, being carried away 

 by the stream, and thrown out at the excretory orifice. 



As nothing until now was known regarding the structure of 

 cilia, everything brought forward as to the cause of their move- 

 ments has been conjecture only. Having found in them a struc- 

 ture adapted for contraction and relaxation, the author has much 

 pleasm'C in thus showing that his fellow-countryman. Professor 

 Sharpey, was right when in the year 1836 he thought it probable 

 that the moving power of cilia lay in the cilia themselves, and 

 was referrible to a substance contained in moi-e or less of their 

 length, like that of muscle. 



The undulatory movements of cilia, — compared by Sharpey, 

 when many were seen together, to those produced by the wind 

 on a field of corn, — the author on two occasions witnessed when 

 performed by cilia in a single line, and when most perfect ; on 

 one of which occasions he had the pleasure of showing the rare 

 spectacle to Pui'kinje. In both instances this living mechanism 

 was seen at the marginal end of the bar, and in the line of cilia 

 m, fig. 41 ; in one instance at the point r, in the other at the 

 point marked s. The rough diagram, fig. 42, will scarcely serve 

 to convey an idea of these undulatory movements, for the ap- 

 pearance was exceedingly delicate and beautiful. The undula- 

 ting cilia in the two instances were in different conditions. In 

 the one instance they had their spirals in a twine-like state, as 

 in fig. 40, and were permanently contracted at no part ; in the 

 other instance they were permanently contracted at the base, as 

 at m in fig. 36. In the first case the movements may have con- 

 sisted merely of a shortening and lengthening in the axis of the 

 cilia J in the second, of flexion at the base. Further, the cilia 

 in the two instances in question were of different forms ; in one 

 instance being straight, as in fig. 40, — in the other curved, as in 

 fig. 36 m. As now the contraction of a double spiral implies a 

 twisting of the same, the extremity when bent must describe a 

 course spirally infundibular, not represented in the diagi-ain. 

 [The author observed very young cilia, fig. 43, which evidently 



