ARCHER, ON DESMID1ACE.E. 221 



exhibits it, must be normal ; this may, however, possibly be 

 due to some modification of the same molecular law, com- 

 bined with intei-nal currents. 



In alluding to internal currents I may mention that I 

 believe this phenomenon occurs in a greater number of 

 Desmidian species than is generally supposed, bat ordinarily 

 in very many it seems to be very rare. Closterium Lunula 

 and Penium digitus, as is well known, scarcely ever fail to 

 show it. But, besides, I believe with care it can be some- 

 times seen in other species of Closterium, as well as other 

 genera besides. I have never seen the rotation, as it is 

 called, more vigorous or more active in any vegetable cell 

 than I have sometimes, though by no means always or often, 

 seen it in Closterium didymotocum, where the granules, car- 

 ried onwards by the current, chased each other, with great 

 vigour, round and round the margin of the cell, up one side 

 and down the other, in a manner scarcely comparable to the 

 fitful and irregular currents in Closterium Lunula. Again, in 

 Micrasterias denticulata I have noticed a few loose granules 

 carried by the current, to travel up and down from one sub- 

 division of a lobe to another, following thus the very zigzag 

 course produced by the deeply incised margin of this species 

 for two or even three of the subdivisions ; when, not being 

 then carried any further round the margin, they were diverted 

 again towards the middle of the frond and joined in the 

 quadrille (I can think of no better word) there performed by 

 other free granules, until, perhaps, again carried off to the 

 margin, or a few different granules being drawn off in their 

 place. I have noticed similar circulating currents in Cosma- 

 rium Raffsii ; in this species, however, the segments, unlike 

 Micrasterias, being not incised, the granules were carried 

 round and round in an uninterrupted stream. This vigorous 

 cuiTent, however, is very rare ; yet I half think I have been 

 able to see currents of the fluid contents in certain Closteria 

 and others, where, at least, it Avas not evidenced by its car- 

 rying any granules with it. But, be this as it may, although 

 I have very frequently witnessed the phenomenon of the 

 active vibratory particles alluded to in very many species, I 

 have never once seen them escape by any normal process. 

 It is true, that when the frond is artificially ruptured, they 

 still, for a time, maintain their movement, though generally 

 less actively ; but I have also noticed many of the granules 

 of the general mass of cell-contents, broken up by pressure, 

 themselves to set up a very similar movement, perhaps not so 

 active, though before, of course, they were still. 



But if further evidence were wanting to prove the point in 



