314 THE MICROSCOPE. 



in the 1200th of an inch ; there can also be traced, in its 

 whole length, a line, by . which, when at maturity, spon- 

 taneous fissuration occurs, and in this manner it preserves 

 its form from age to age. 



COLLECTING AND PRESERVING DIATOMACECE. The Rev. 

 W. Smith's directions for collecting and preserving the 

 Diatomacece will prove of use to the student : " Let him 

 provide himself, in the first place, with the necessary ap- 

 paratus for the field : this includes a good stock of small 

 wide-mouthed bottles, that each gathering may be kept 

 perfectly distinct ; a long rod or stick, to which can be 

 attached a small muslin net; a cutting-hook of about 

 three inches in length, and a broad flat spoon ; the first, 

 to collect such specimens as float upon the surface, or are 

 held in suspension by the water ; the second, to remove 

 the larger Algce which may be covered with parasitic Dia- 

 toms ; and the third, to skim the surface of the mud for 

 those which lie at the bottom of the pool. 



" He will probably find, notwithstanding every care, that 

 his specimens are mixed with much foreign matter, in the 

 form of minute particles of mud or sand, which impair 

 their value, and interfere with observation, especially with 

 the higher powers of his instrument. These substances 

 the student may remove in various ways : by repeated 

 washings in pure water, and at the same time, profiting by 

 the various specific gravities of the Diatoms and the inter- 

 mixed substances, to secure their separation; but, more 

 particularly, by availing himself of the tendency which the 

 Diatomacece generally have to make their way towards the 

 light. This affords an easy mode of separating and pro- 

 curing them in a tolerably clean state ; all that is neces- 

 sary being to place the gathering which contains them in 

 a shallow vessel, and leave them undisturbed for a suffi- 

 cient length of time in the sunlight, and then carefully 

 remove them from the surface of the mud or water. 



" The simplest method of preserving the specimens, and 

 the one most generally useful to the scientific observer, is 

 simply to dry them upon small portions of talc, which can 

 at any time be placed under the microscope, and examined 

 without further preparation ; and this mode possesses one 

 great advantage, that is, that the specimens can be sub- 



