ERY OP TRIPOLI OR POLISH (NO POWDER, 



TKKMINOLOar. 

 The Htnictural plan of a Diatom in not very 

 oompUcatec], In each Beparate individual or 

 "frnstule," the oa«e conHiHtx of two Hymmetri- 

 cal halves or "vUveH" joined to^ethtr l>y their 

 ed^reH, (Hotnetinies with an intermediate piece 

 or "huop" interpoHed) which line <>f junction 

 is termed the "miture." The circular forms 

 ma^ he likened to a very shallow pillbox of 

 which the upper and lower halves represent 

 the valves, their opposed ed^'es the suture and 

 the body of the box the hoop. If we suppose 

 the shape of the box to be trianKular instead 

 of circular we shall have a Trinratium, if 

 acutely oval a Navicula, and so on. The 

 valves bein^ always more or less concavo-con- 

 vex, recede from each other so as to enclose a 

 space which is filled by the jelly-like substance 

 called the "endochrome," whose color in the 

 living individual is usually a rich yellowish 

 brown. This color is supposed to be clue to the 

 presence of a minute proportitm of iron which 

 always enters into the composition ci this 

 plant As the valves vary^ieatly in the shape 

 and extent of their convexity we cannot get a 

 clear idea of the shape of any particular Dia- 

 tom until we have obtained at leattt two differ- 

 ent views of it, one by looking at the surface 

 of the valve, and the other by looking at the 

 suture, the former of whiih is called in dexcrip- 

 tion the "side" and the latter the "front" view. 

 These views are never (piite sindlar and they 

 are o^ten bo widely different that it would be 

 quite impossible to inter one of them from the 

 other; hence in order to know any one form 

 correctly we must become ac(|uainted with at 

 least two quite dissiunlar appearances, u fact 

 which often causes great perplexity and con- 

 fusion to the beginner. It can readily be l>e- 

 lieved that when these forms tirKt began to be 

 examined and named, the front and side viewf 

 of the same Diatom were in more than one in- 

 stance described as two different species. 



SURFACE MAKKINO». 



The surfaces of the valves are seldom smooth 

 but are almost always diversified with various 

 kinds of elevations, depressionx. Hues, dots, 

 ets., which are often arranged in complex and 

 very b lautiful patterns. These si.rface mark- 

 ings have received a good deal of attention 

 from microscopists. Some of them present no 

 difficulties of interpretation to the observer, 

 while long and often angry controvernies have 

 been held as to the precise nature of others. It 

 would be a difficult matter to compute how 

 much midnight oil, how many hours of pati- 

 ent labor, how many reams of paper and pints 

 of ink have been expended in attempting to 

 settle such questions as whether certain of 

 these surface marks are rcially to be considered 

 as transparent knobs or as holes ?— whether 

 the valve of a certain species is marked by 

 100,000 fine striations to the inch or only 75,- 

 000 ?— whether the minute dots into which 

 certain of these lines are resolvable are really 

 elevations or depressions ? etc. All these seem- 

 ingly trivial controverKies have not been with- 

 out great practical usefulness, for to them are 

 largely owing the extensive and important im- 

 provements that have been effected within the 

 last twenty or thirty years in the construction 

 and Uae of high power object glasaes and the 



application of new and elaborate methods of 

 iluiminatiun to objects viewed under the mic* 

 roscope. 



•' TK8T " DIATOMS. 



Until quite recently certain of tneae Diatom- 

 valves were in use as the standard tests of the 

 resolving power of high class objectives, and 

 even the introduction of M. Nobert's ruled 

 bands has not entirely abolished their use for 

 this pur|)ose. Most microscopists still keep 

 stowed away somewhere in their cabinets a |)et 

 valve or two which require the use of high 

 powers combined with elaborate illumination 

 and much manipulative skill to " show tha 

 lines" in all their glory. But all this minute 

 refinement of detail lielongs more to the pro- 

 vince of the optican than to that of the natur- 

 Hlist. I need (miy say here that the surface- 

 marking of the l>iatoui8 are always pretty and 

 often quite elaborate, and that combined with 

 the geometrical outline and symmetry of the 

 valve they render it a most attractive object to 

 the eye. I have here some rouxh diagrams to 

 illustrate a few of the forms that .tre most 

 commonly met with, and under the microscopes 

 tipon the table you will see other forms which 

 will fully bear out the character that I give 

 them. 



AUTt»MATIC MOTIONS. 



Like some others of the lower forms of vege- 

 table life, the Di ttouis possess the power of 

 automatic motion, which, until not very long 

 ago, vas thought to be an attribute peculiar to 

 the animal kingiloin. The motion that they 

 exhibit is of variout kinds. In the discoidal 

 ikud equilateral forms it is a mere languid roll 

 from side to side and progress is made but very 

 slowly. In the elongated forms the frustule ad- 

 vances for a cer''iin length of time in the dir- 

 ection of one of its extremities, then pau'iea 

 an<l moves for a similar period in the direction 

 of the other. If we may judge from the quan- 

 tity of loose debris and floating particles that 

 the Diatom can drag along with it, these mo- 

 tions appear to be exerted with considerable 

 power. If, however, an obstacle be encounter- 

 ed which is too heavy to be pushed aside or 

 carried along with it, the diatom remains press- 

 inif against it until its regular period for ad- 

 vancing in that direction has expired and then 

 back^ off in the opposite directicm. Sometimes 

 the motion consists of a series of intermittent 

 jerks and sometimes it is a steady and equable 

 progression. 



BACILLARIA. 



One very curious form, BaciUaria Paradoxa, 

 which anybody who wishes to examine it can 

 make tolerably sure of finding in Little River 

 marsh, not far from our city, consists of from 

 about ten to t""^nty long narrow frustules laid 

 one upon ano dr, and, when mcMsed together, 

 suggesting in appearance the slats of a Veneti- 

 an blind. At intervals these frustules slide 

 over and away from each other until they are 

 almost detached and the rectangular mass or 

 battalion is drawn out into a long chain of rods 

 just touching aud overlapping each other by 

 the comers and apparently upon the point of 

 pulling apart from each other altogether. This 

 event, however, never happens, for when the 

 limit has been reached the frnstules all slide 



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