Spiral Structure of Muscle. 179 



They contained at the margin numerous cells. The middle 

 space presented none. On the nature of these large fragments 

 the author has for the present nothing further to remark, than 

 that they afforded him an invaluable contribution towards the 

 history of development of cilia ; for of that development they 

 presented with distinctness a very early stage. The minute cells 

 in their interior seemed destined to give origin to cilia, which 

 here and there, fig. 29, were seen to have been already formed 

 and to have burst through the membrane of their cells. One of 

 these, the interior of which was seen with rare distinctness, is 

 represented on a larger scale in fig. 30. The young cilium here 

 drawn consisted of two spirals, within the winds of which was a 

 pellucid substance corresponding to that which the author above 

 and elsewhere has termed hyaline. At the extremity the two 

 spirals passed into one another, and were bent over hook -like 

 towards one side. At the base they separated, to bestride, as it 

 were, the contents of the cell in which the cilium had been 

 formed*. Perhaps these two separate threads may be considered 

 as the radical ends of the cilium, in which growth tu'st of all 

 takes place somewhat in the following manner : — The extremity 

 of each of these two threads draws into itself new substance from 

 the nucleus of the cell. And now as the cilium is alternately in 

 the states of twisting and untwisting, it gradually spins up into 

 its substance those after-threads, and in this manner elongates. 

 Drawings are then given of stages following those just de- 

 scribed, of which figs. 31, 32, 33, and 34 present a selection. 

 These different appearances evidently denote different degrees of 

 development. [Corresponding differences were noticed in their 

 movements. None of them, however, were in a perfect state. 

 For the movements of even the most advanced were awkward, 

 showing them to be, as it were, still in their apprenticeship.] 

 Now to all of these cilia, making allowance for differences in the 

 degree of development, may be applied the description just given 

 of fig. 30 ; though it is only here and there that a trace of con- 

 nexion with the cell, such as that in fig. 30, can be distinctly 

 seen. The author thinks that no observer can attentively examine 

 such cilia without seeing, as he did, that each of them consists of 

 a double spiral thread, having therefore a structure like that of 

 the muscular fibril, and thus estabhshing his position No. 1. 



The broad cilia of which examples have been given in Beroe 

 and other ciliograde MoUusca, — where, instead of cilia of usual 

 form and arrangement, there arc found rows of broad flat flaps 

 each of which is said to consist of a row of single cilia, — appear to 



* [It will be observed, that each of these separate threads is twisted on 

 itselfrj 



N2 



