178 Dr. Barry's renewed Inquiries concerning the 



Before detailing his obseiTations, the author states what others 

 should do who may be disposed to repeat the examinations. A 

 small piece, about a square line, hanng been cut from the mar- 

 ginal edge of the gill and placed upon glass, he adds to it a drop 

 of the fluid, which, on the mussel being opened, collects in the 

 shell, gently and to a small extent separates the bars from one 

 another with fine needles, and places them under the microscope 

 without the addition of any covering such as glass or mica. It 

 is soon seen that some of the bars, wedge-like in their transverse 

 sections, present the thicker of their edges to the eye, fig. 37, 

 while others are lying on theii" sides, figs. 41, 36. Both should 

 be examined with especial reference to the cilia on the two sides 

 of the bar. Of these cilia there are three sets, and not two only, 

 as hitherto supposed ; one set uppermost when the thicker edge 

 of the bar is directed towards the eye, and marked m in the 

 figui'es just referred to ; the second occupying a middle place, 

 and marked n in the same figures ; the third lowest, and marked o. 



Concerning these cilia, the author states the following as new 

 facts : — In the fii'st place, these cilia, and from analogy probably 

 all cilia, consist of double spiral threads, and thus have a struc- 

 ture like that of the muscular fibril ; secondhj, the cilia /», fig. 36, 

 &c., present merely stages in the development of the cilia n ; 

 thirdly, the cilia o, in the same figures, hitherto either overlooked 

 or held to be identical with the cilia n, are really not so, — they 

 are the counterpart thereof. And he then proceeds to establish 

 these three positions in the order here laid down, as follows : — 



Separated from their localities by manipulation, and strewn 

 through the field of view among the fragments of the gill, are 

 seen simple cells, several of which are represented in outline in 

 fig. 27. In the interior of such cells the young cilia are indi- 

 cated. They push before them the membrane of the cell, so 

 that it appears pointed; and afterwards present themselves, as 

 in fig. 28, of a club-like form*. Sometimes this club-like form 

 appears referrible to a provision of plastic substance at the ex- 

 tremity for the lengthening of the ciliura, and sometimes to a 

 bending down of the extremity hook-hke upon itself. Up to 

 this time the membrane of the cell appears in some instances to 

 continue entire, — the young cilium, though coming into view, 

 being as it were still unborn. At length the membrane is rup- 

 tured, and the bent down extremity of the cilium gradually de- 

 velopcs and unrolls itself like a young fern, fig. 29. This figure, 

 fig. 29, represents part of a large fragment, several of which 

 were found in substance scraped from the gill of the Oyster. 



* Probably Valentin saw the same stage of development in Unio jnctorum, 

 where he meutious it (the " club-hke form "J as au uuusual shape (" aus- 

 nahmsweiser Gestalt"). — R. Wagner's Handworterbuch der Physiologie, 

 p. 600. 



