28G THE MICROSCOPE. 



break away, and are carried by the circulation of the fluid, 

 which works all over the endochrome, to the chambers at 

 the extremities ; there they join a crowd of similar bodies, 

 each in action within those chambers 3 when the specimen 

 is a healthy one. 



The circulation, when made out over the centre of the 

 frond, for instance at a, is in appearance of a wholly 

 different nature from that seen at the edges. In the 

 latter, the matter circulated is in globules, passing each 

 other, in distinct lines, in opposite directions ; in the cir- 

 culation as seen at a, the streams are broad, tortuous, of 

 far greater body, and passing with much less rapidity. To 

 see the centre circulation, use a Gillett's illuminator and 

 the l-8th power ; work the fine adjustment so as to bring 

 the centre of the frond into focus, then almost lose it by 

 raising the objective ; after this, with great care, work the 

 milled head till the dark body of the endochrome is made 

 out ; a hair's-breadth more adjustment gives this circula- 

 tion with the utmost distinctness, if it is a good specimen. 

 It will be clearly seen, by the same means, at all the 

 points where the spaces are put ; 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 uninter- 

 rupted clear spaces visible between the green matter and 

 the investing membrane ; at other times, the endochrome 

 is seen with a straight margin, but so contracted as to 

 leave a well-defined transparent space along its whole edge, 

 between itself and the exterior case. It is interesting 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. 



At B is 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, 

 which can be detected, and occasionally traced, most dis- 

 tinctly ; it is acted upon by cilia at the edges of the 

 chamber, but its chief force appears to come from some 

 impulse given from the very centre of the endochrome. 



