XX ERRATA AND ADDENDA. 



cimens for mounting. In such cases a small portion of the mass 

 should be mixed with a little of the creosote fluid, and stirred briskly 

 Avith a needle. After this has been done the Desmidiese will sink to 

 the bottom, when the refuse should be carefully removed. Successive 

 portions having been thus treated, specimens will at length be pro- 

 cured sufficiently free from foreign matter. Even in ordinary circum- 

 stances, if a small extra quantity of fluid be placed in the cell, and 

 the slide gently inclined, most of the dirt can be removed by a 

 needle before the cell is closed, which process will materially increase 

 the beauty of the preparation. 



If the cells are insufficiently baked, the japan occasionally peels off 

 the glass after the specimen has been mounted for some time. To 

 obviate this inconvenience, Mr. Jenner previously heats the cell, with 

 much caution, over a rushlight, until the japan becomes of a dark 

 colour, and vapour ceases to arise from it. 



When gold-size is used for closing the cell, the intrusion of some 

 of it frequently destroys valuable specimens, whatever care may be 

 taken : Mr. Jenner has therefore relinquished it, and now employs a 

 varnish made of coarsely comminuted purified shell-lac or translucent 

 sealing-wax, to which is added rectified spirits of wine, in sufficient 

 quantity to cover it. This varnish will be ready for use in about 

 twelve hours ; when it is too thick a little more spirit should be 

 added. Mr. Jenner applies three coats of this varnish, and about a 

 week afterwards a fourth composed o^ japan varnish or yold-size. 



I have tried this method extensively, and have never found my 

 specimens spoiled by the varnish insinuating itself into the cell. This 

 process requires less time, and herein it possesses another great ad- 

 vantage over the gold-size method, for the second coat being applied 

 vidthin half an hour, the risk of admitting air into the cell is much 

 diminished. 



To preserve the brush in a fit state it should always be cleaned 

 with spirits of wine whenever it has been used. 



At page 16 of the Introduction I have stated that I had never wit- 

 nessed the circulation in the Closteria ; but since the printing of that 

 part Mr. Bowerbank has shown me the circulation in Closterium Lu- 

 nula and in Penium Digitus. It seems, at least in the Closterium, to 



