Dr. Barry's further Remarks on the Muscularity of Cilia. 373 



phibia, from a like pushing forth of the cell-wall by the fibre 

 given off by the nucleus in those cells. And when the extremity 

 of the cilium is free, fig. 9, there is still to be recognized in the 

 bent form of young cilia a trace of that in which the nucleus 

 gave them off. 



Every cilium is a twin spiral, like the muscular fibril. Fig. 9, 

 a drawing from nature, represents a young cilium from the gill 

 of the common Oyster, in the form in which it proceeds from its 

 cell. At the extremity its two spirals pass into one another, and 

 are bent over hook-like towards one side. At the base they 

 separate, to bestride as it were a bulb consisting of minute pel- 

 lucid globules of high refractive power. These globules I have 

 elsewhere termed the contents of the cell, and such they are. 

 More particularly considered, however, they represent the re- 

 mains of the nucleus of the cell resolved into globules. The two 

 after-threads derive their nourishment from, or rather they are 

 formed by the globules in the bulb. The bulb thus gradually 

 becoming exhausted diminishes in size, and at length entirely 

 disappears. Hence it was that I found the bulb at the base of 

 some cilia much smaller than at that of others. Hence, too, an 

 explanation of the cause why some observers have denied the 

 existence of a bulb ; their attention having probably been directed 

 to cilia from which the bulb had disappeared. 



The two after-threads may perhaps be considered as the roots 

 of the cilium, in which it has its early growth. The extremity 

 of each of them takes up new substance from what had been the 

 nucleus of the cell, while the cilium, by its rotatory movements, 

 which consist in twisting and untwisting (contraction and relax- 

 ation), spins up the after-threads — its early mode of elongation. 

 For this the after-threads are prepared by their spiral form, 

 which also seems to be a provision for rendering the elongation 

 of the cilium rapid. It will be seen from the figure that each 

 after-thread is a single spiral, being twisted on itself; and that 

 the direction of the spiral winds is in both of them the same ; 

 the same, moreover, as that of the twin spirals of the cilium of 

 which the after- threads are continuations. Very few movements, 

 therefore, of the kind just mentioned sufficed to apply to one 

 another these after-threads, and thus to make them part of the 

 cilium itself. 



I have presented a model in lead wire of the muscular fibril, 

 and of a young cilium such as that in fig. 9, to the Royal So- 

 ciety, to the Museum of the Royal College of Surgeons in Lon- 

 don, to the Royal Society of Edinburgh, to various colleges and 

 museums in Edinburgh, and to the Museum of Physiology in 

 the University of Prague. 



