326 NATURAL HISTORY OF OUR SHORES 



are bright and transparent they can be lifted out with the 

 forceps, laid nice and flat on the centre of the slip, the 

 superfluous oil drained off, and Canada balsam applied. 

 Cover and finish as before directed. The celloidin, although 

 it shows like a little leaf of gelatine around the section, and 

 between the parts of the object, where it holds them to- 

 gether, will be invisible when the slide is finished. 



Beautiful sections of the sponges, to show spicules, etc. ; 

 also sections of such things as the compound ascidians ; 

 the columns of anemones, to show the radiating mesenteries, 

 etc. in fact, anything where the minute, histological de- 

 tails, for high powers, are not needed can be mounted. 



It will occur to the reader " What about the dense masses 

 of flint spicules in the sponges ? " These do not trouble 

 a bit : the razor passes freely through all, and only gets 

 blunted a little, but the oil-stone must be kept at hand to 

 touch up the edge pretty frequently. 



Mounting Zoophytes and Polyzoa with Tentacles extended. 

 Methods for killing these in a state of extension have been 

 given in the chapter on preserving museum specimens. 

 This is the plan to be followed, only that, after they are 

 anaesthetised, they should be fixed. 



A few drops of osmic acid, or a strong solution of corrosive 

 sublimate should be added to the water in which they 

 are ; or they can be placed for a while in some 

 Bouin's fluid (see page 319), Then wash them in fresh 

 water ; place them in rather dilute stain ; wash again 

 in water, and pass through grades of spirit up to 

 absolute alcohol. 



Then select the desired branches, and place them to clear 

 in a little pot, with oil of cloves. (Never allow these, or, in 

 fact, any other thing, to dry between the changes of media.) 



They should be mounted in a " sunk- cell slip," without 

 being pressed or distorted. Fill the sunk cell well with 

 balsam and benzole, in fact, overfill it, or you will get an 



