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The specimen before us is the most regular in its crystalli- 

 sation I have ever seen. I think the variations in crystalline 

 form found in many of these nearly pure forms of Silex are 

 produced by the varying rate at which they have cooled, doubtless 

 combined with other causes. It is certain, however, that the 

 various modifications exhibited in them may be produced in many 

 mineral salts by variations in the amount of heat used, and the 

 rapidity or slowness of cooling, as I have personally found. It is 

 to the prevention of natural crystallisation that so many of our 

 pretty polariscopic slides owe their character. I know much may 

 be said against the igneous origin of Chalcedony, and that I have 

 taken for granted, both, that it is a modified crystalline form, and 

 produced in part by heat ; but I think what I have seen, (and 

 doubtless other members who may have tried their hands on 

 crystallising mineral salts have seen the same,) warrants the suppo- 

 sition that agate, in many of its forms, is the result of crystallisa- 

 tion, modified by variations of heat and other surrounding con- 

 ditions. 



D. Moore. 



Antennae of Cockroach. — I have counted 74 or 75 joints in 

 each antenna. 



R. H. Moore. 



Tracheal System of Caterpillar.— Quekett's method of pre- 

 paring these objects with acetic acid I have found very un- 

 satisfactory. My slide was prepared thus : — Having cut off the 

 head of the caterpillar, and made an incision down the back, I 

 placed it in a solution of sub-carbonate of potash and lime (Z/^. 

 Fof. would do). In three or four days the body had become of a 

 hard, cheesy consistency. It was then easy to turn it out of the 

 skin with a blunt knife. Boiling in potash for a few hours dis- 

 solved the mass (which, by the bye, I had gently crushed), and 

 the trachea was left floating in the liquid. After washing well, it 

 was floated on to the slide. 



Thos. Lisle. 



Trachea of Caterpillar.— Mr. Lisle's process, as described 

 above, is certainly the best and easiest. But I do not think that 

 boihng is necessary, as I have procured good specimens by steep- 

 ing only in Z/^. Pof. (strong solution) for four or five days. After 

 that take the insect out of the solution, place it in a shallow dish 



