2G DUBLIN NATURAL HISTOEY SOCIETY. 



noticeable. This, then, in all such examples I should be inclined to 

 imagine is a manifestation of the phenomenon called " molecular move- 

 ment," similai^ to that noticeable in the granules of the fo villa of pollen 

 in the flowering plants, or to that seen when a small portion of the sub- 

 stance of the common fresh- water sponge is crushed down and viewed 

 under the microscope (and of this other examples might be cited), and 

 rather in the cases so common in the Desmidiacese, and in the very rare 

 examples referred to in the Diatomaceae, indicative of decay, than as the 

 precursor of a further developmental change. I do not, of course, in- 

 clude the singular movement of the free, active particles at the extremi- 

 ties of Closterium, Docidium, &c., which, as every specimen of the 

 species in which it occurs exhibits it, must be normal ; this may, how- 

 ever, possibly be due to some modification of the same molecular law, 

 combined with internal currents. 



In alluding to internal currents I may mention that I believe this 

 phenomenon occurs in a greater number of Desmidian species than is ge- 

 nerally supposed, but 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 sometimes 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 diclymotocum, where the granules, carried 

 onwards by the current, chased each other, with great vigour, round and 

 round the margin of the ceU, up one side and down the other, in a man- 

 ner scarcely comparable to the fitfal 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 subdivi- 

 sion 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 fui'ther 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 simi- 

 lar circulating currents in Cosmarium Ralfsii ; in this species, however, 

 the segments being not incised, as in Micrasterias, the granules were car- 

 ried round and round in an uninterrupted stream. This vigorous cur- 

 rent, however, is very rare ; yet I half think I have been able to see cur- 

 rents of the fluid contents in Closteria and others, where, at least, it was 

 not evidenced by its carrying 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 veiy 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 thefr move- 

 ment, though generally less actively ; but I have also noticed many of 

 the granules, broken up by pressure themselves, to set up a very similar 

 movement, perhaps not so active, though before, of course, they were 

 still. 





