44 



THE AMEEICAI^ MONTHLY 



[March, 



indicate that the frustules are envel- 

 oped in a membrane, and such I be- 

 lieve to be the case. This envelop- 

 ing membrane, if adhesive, would 

 cause many of the appearances noted, 

 provided the motion be accounted 

 for; but adhesiveness of the diatom 

 would not of itself cause motion. I 

 have often seen a small diatom mov- 

 ing along beside a much larger, sta- 

 tionary one,, cause the latter to re- 

 volve by the friction, often partly 

 overturning it. But in the cases 

 where extraneous matter is seen ad- 

 hering to, or trailing after a diatom, 

 how do we know that the adhesive 

 property does not reside in the ad- 

 hering matter and not in the diatom 

 at all ? I have often seen such masses 

 of flocculent matter adhere to entomo- 

 straca and rotatoria when they hap- 

 pened to brush against it, and re- 

 main attached some time until detach- 

 ed by the violence of their movements. 

 The remarkable alternation of mo- 

 tion seems to me a very strong objec- 

 tion to the ciliary theory, and equally 

 so to that of the prehensile filaments. 

 No other ciliated or flagellate organ- 

 ism that I know of exhibits such al- 

 ternation, but whether animal or vege- 

 table, when free to move they swim 

 hither and yon in a purposeless and 

 indefinite course, without limit. But 

 if prehensile filaments exist, they 

 should, to be in accord with other 

 provisions of nature, bear a relative 

 proportion in size to the diatom by 

 which they are borne. Yet, in large 

 diatoms, like Amphiprora ornata^ Su- 

 rirella splettdida, S. turgida, etc., when 

 active and moving with great force, no 

 trace of cilia, pseudopodia, filaments 

 or anything of the kind has yet been 

 discovered. I have watched a large, 

 thick Surirella plowin g its way through 

 tangled masses of Tabellaria, and 

 sweeping before it masses larger than 

 its own bulk, and hoped to find some 

 trace of the means by which the re- 

 sistless motion was imparted, but 

 without success, although I brought 

 to the task objectives capable of 

 resolving the Amphipleura pellucida. 



No trace of currents, of cilia, or any 

 external appendages could be seen, 

 nor any motion in the endochrome 

 of the diatom. I have also observed 

 that these large diatoms do not show 

 the same attraction towards loose 

 particles in the water which the small- 

 er ones do. 



I have seen living diatoms, both 

 still and moving forms, with a sub- 

 stance adhering to them which had 

 exactly the appearance of a fragment 

 of an amoeba, but without the move- 

 ment natural to the latter. And I 

 have seen the same substance adher- 

 ing to dead diatoms entirely free 

 from endochrome. In all the cases I 

 am convinced it was foreign to the 

 diatom and had no connection with 

 the motion of the diatom to which it 

 adhered. 



Most diatoms, even when unobstruct- 

 ed, move with a quivering or stagger- 

 ing motion, much like a drunken 

 man, which does not seem consistent 

 with ciliary action, or with currents 

 produced by osmotic action, and be- 

 sides we should expect the currents 

 produced by cilia or any other force 

 capable of moving the diatom, to be 

 strong enough to move adjacent par- 

 ticles when the diatom is held fast. 

 Yet we do not see free particles moved, 

 or any evidence of current in the wa- 

 ter except where there is contact with 

 the diatom. Frequently we see a 

 small mass moving along the diatom 

 while another mass, apparently in con- 

 tact with it, is not affected until the 

 moving mass strikes the stationary 

 one, when both move as one, or as if 

 stuck together by some adhesive sub- 

 stance. 



The appearance mentioned by Mr. 

 Mills, of a clear space surrounding 

 diatoms like Cyclotella is not an inva- 

 riable characteristic. I have seen the 

 complete space around some frustules, 

 while others of the same species in 

 the same gathering were matted with 

 light stuff, and often themselves mat- 

 ted in groups, while all, judged by 

 the appearance of the endochrome, 

 were equally alive and vigorous. In 



