56 ON THE ECONOMY OF CLOSTERIUM LUNULA. 



make out the dark body of the endochrome ; a hair's-breadth 

 more adjustment gives me this circulation with the utmost 

 distinctness if it is a good specimen. It will be clearly seen, 

 by the same means, at all the points where I have put spaces, 

 and from them, may be traced, with care, down to both 

 extremities. 



The endochrome itself is evidently so constructed as to 

 admit of contraction and expansion in every direction ; at 

 times the edges are in semi-lunar curves, leaving interrupted 

 clear spaces visible between the green matter and the investing 

 membrane ; at other times, I have seen the endochrome with 

 a straight margin, but so contracted as to leave a well-defined 

 transparent space, along its whole edge, between itself and 

 the exterior of its sac. It is interesting, in this case, to 

 keep changing the focus, that at one moment we may see the 

 globular circulation between the outer and inner case, and 

 again the mere sluggish movement between the inner case and 

 the endochrome. 



I have now not the slightest doubt but that the loose bodies 

 in the chambers at each extremity of the frond are brought, 

 as I have described above, from the exterior of the endo- 

 chrome, by the external current ; what they are I do not 

 profess to say ; they are as the rule diamond-shaped, when 

 at rest. 



In B, I have given an enlarged sketch of one extremity of 

 a C. Lunula. The arrows within the chamber pointing to b, 

 denote the direction of a very strong current of fluid 1 can 

 detect, and occasionally trace most distinctly ; it is acted 

 upon by cilia at the edges of the chamber, but its chief force 

 appears to me to come from some impulse given from the 

 very centre of the endochrome. I have seen the fluid here 

 acting in positive jets, that is with an almost arterial 

 action ; this it is, which, according to the strength with which 

 it is acting at the time, propels the loose floating bodies at 

 a greater or less distance from the end of the endochrome ; 

 the fluid thus impelled from a centre, and kept in activity 

 by the lateral cilia, causes strong eddies, which give the 

 twisting motion we see to the said free bodies. The line 

 — a, in this diagram, denotes the outline of the membrane 

 which encloses the endochrome ; on both sides of this I can 

 detect cilia. The circulation exterior to it passes and repasses 

 it in opposite directions, in three or four distinct courses of 

 globules ; these, when they arrive at — c, seem to encounter 

 the fluid jetted, through an aperture at the apex of the 

 chamber; this disperses them so that they appear to be 



