602 THE MICROSCOPE. 



Mr. Norman, of Hull, has favoured me with the follow- 

 ing : 



"HINTS TO COLLECTORS OF DIATOMACE^E. 



" These minute forms are found in all waters, but the 

 most interesting species are those found in salt water, 

 especially shallow lagoons, salt water marshes, estuaries of 

 rivers, pools left by the tide, &c. 



" Their presence in any quantity is always shown by the 

 colour they impart to the aquatic plants and sea-weeds 

 they are found attached to, and if found on the rnud, 

 which is very frequently the case, they impart to it also a 

 yellowish brown colour approaching to black brown, if in 

 great numbers. 



"This brownish pellicle, if carefully removed with a 

 spoon (without disturbing the mud) will be found very 

 pure. Capital gatherings of Diatomacese might be obtained 

 by carefully scraping the brown coloured layer from moor- 

 ing posts, and piles of wharfs and jetties. 



" In clear running ditches the plants and stones have 

 often long streamers of yellowish brown slimy matter 

 attached to them, which is generally entirely Diato- 

 maceous. 



" When found in large quantities on the mud the layer 

 is often covered with bead-like bubbles of oxygen. This 

 often detaches them from the bottom and buoys them to 

 the surface, where they form a dense brown scum, which 

 is blown to leeward in large quantities, and presents the 

 general appearance of dark-coloured yeast. 



" In this form it may be collected in abundance, often 

 quite free from particles of sand and other impurities. 



" Good and rare species have been obtained from the 

 stomachs of oysters, scallops, and other shell-fish inhabiting 

 deep water. 



" The sea-cucumbers (Holothuridee) found so frequently 

 in southern latitudes contain many species. 



" These animals might be simply dried and preserved 

 just as found, and the contents of the stomach afterwards 

 obtained by dissection. 



"The Noctilucse which cause the phosphorescence in 

 the sea are Diatom feeders, and might be caught in large 

 quantities in a fine gauze towing-net, and preserved. 



