6 INTRODUCTION. 



by the old ways of mounting, that, becoming disheartened, I gave up all idea of 

 making a permanent cabinet, until a new cement, invented by Dr. J. G. Hunt, of 

 this city, was brought to my notice. This is prepared as follows: — 



" Take damar gum, any quantity, and dissolve it in benzole; the solution may be 

 hastened by heat. After obtaining a solution just thick enough to drop readily 

 from the brush, add enough of the finest dry oxide of zinc— previously triturated 

 in a mortar with a small quantity of benzole— until the solution becomes white 

 when thoroughly stirred. If not too much zinc has been added, the solution will 

 drop quickly from the brush, flow readily, and dry quickly enough for convenient 

 work. It will adhere, if worked properly, when the cell-cover is pressed down, 

 even when glycerine is used for the preservative medium. Keep in an alcohol- 

 lamp bottle with a tight lid, and secure the brush for applying the cement in the 

 lid of the bottle." 



Its advantages lie in the circumstance, that the glass cover can be placed upon 

 the ring of it whilst still fresh and soft, and that in drying, it adheres to both cover 

 and slide, so as to form a joint between them of the width of the ring of cement, 

 and not, as with asphaltum, gold size, &c., simply at the edge and upon the outside 

 of the cover. It is readily to be seen how much less liability to leakage must 

 result from this. The method of mounting with it is as follows: A ring of any 

 desired size is made, by means of an ordinary Shadbolt's turn-table, upon a slide, 

 which is then placed to one side to dry. When required for use, the specimen, 

 cover, &c., being all prepared and ready, the slide is again placed upon the turn- 

 table and a new ring of cement put directly upon the old one. The specimen is 

 immediately placed within the ceU thus formed, and the requisite quantity of the 

 carbolated water placed upon it. The cover, which must be large enough to entirely 

 or nearly cover the cement ring, is now picked up with the forceps, the under side 

 being moistened by the breath to prevent adhesion of air-bubbles, and placed care- 

 fully in position. It is now to be carefully and equably pressed down with some 

 force. By this, any superfluous water is squeezed out and the cover is forced down 

 into the cement which rises as a little ring around its edge. The pressure is best 

 made with a stiff" needle, at first on the centre and then upon the edges of the cover, 

 which may finally be made slowly to revolve underneath the needle point. The 

 slide may then be put aside to dry ; or, better, an outside ring of the cement thrown 

 over its edge in the usual manner. Where a deep cell is required, several coats of 

 the cement should be placed one over the other, each being allowed to dry in 

 turn. If time be an object, and only a shallow cell be necessary, the first ring of 

 cement may be dispensed with, and the whole mounting of the specimen be done 

 in a few minutes. Even with this cement and the utmost care in mounting, the 

 cabinet should be occasionally inspected, for there will always be some slides into 

 which air will penetrate. When such are found, eff'orts may be made to stop the 

 leak by new rings of cement overlaid upon the old, but very often entire remount- 

 ing of the specimen is the only satisfactory cure. 



The classification which I have adopted in this memoir is that of Professor Ra- 

 benhorst. I have finally selected it, not as being absolutely natural, but as conve- 

 nient, and as rarely doing much violence to the natural relations of the various species. 



