l886.] NEW-YORK MICROSCOPICAL SOCIETY. 141 



language less pellucid than obscure, tell us that it is a sporangium 

 — that it is now a different organism from what it was before 

 and is destined to emit spores or seed-like bodies capable of 

 starting fresh generations of its kind. Whether this sporangium, 

 having cast its spores, then dies, or lives to start another round 

 of those cell-divisions which beget the mother valves larger than 

 the daughter valves, in a series constantly decreasing in size, 

 I do not know. 



Sixth. A word as to the movements of these little bodies : A 

 Navicula in motion looks exactly like a two-prowed boat. It 

 moves in the water in a straight line, pushing aside obstacles 

 that lie in its path, until, for no apparent reason, it stops, then 

 suddenly moves straight backward. As yet, this movement is 

 a mystery. There is, at times, observable when the diatom is 

 in motion, a white line or coma of light all round the tiny boat, 

 which looks like the effect that would be caused by the oars of 

 an infinitesimal trireme. But no microscopist has ever seen 

 the oars of the diatom. Bacillaria paradoxa has motions more 

 remarkable than mere progression and retrogression. These 

 diatoms are associated in ribbon-like bands of tiny rods, each 

 rod or frustule being an independent individual. "These 

 frustules slide over each other in one direction until they are all 

 but detached and then slide as far in the opposite direction." 

 Their movements are apparently contrary to all known laws of 

 motion. In some of their positions they look like a flight of 

 stairs, in others, like fasces ; in some, not unlike the staves of a 

 barrel, a spiral flight of stairs, &c. From such positions they 

 will quickly fall back into the communal ribbon or band. 



Seventh. The motions of the diatoms induced the belief 

 among earlier observers that these organisms are of an animal 

 nature, a notion which spectrum analysis, it seems to me, entirely 

 sets aside. Ehrenberg believed that the pair of spots usually 

 seen in a diatom, tech ically called the oil globules, were 

 stomachs, and hence designated the order, Polygastri' a. He 

 defended this interpretation of the spots by stating that he had 

 placed indigo in the water containing diatoms, portions of which 

 he subsequently detected in these stomach-like places. Many 

 of us remember the tradition which tells us that years ago the 

 rosy-hued hydrangea when watered with indigo-water pro- 

 duced blue-colored flowers. The indigo experiment proved 



