HARDWICKE'S SCIENCE-GOSSIP. 



17 



length of time, his "practice" will then upset my 

 "theory." I, in common perhaps with others of 

 your readers, would be glad to hear whether the 

 slide of ova of one of tlie mollusca mentioned at the 

 end of his communication, was mounted in a strong 

 alcoholic solution or otherwise, as unless it was so, 

 it cannot fairly be brought forward as an example of 

 durability. I note that very many of your correspon- 

 dents speak of "zinc white" cement; unless tliey 

 prepare it themselves they cannot speak positively as 

 to its composition ; but my belief is that in very many 

 instances this cement is really a " flake white " which 

 is incomparably the better " drier." I make my own 

 white cement and write from experience. — H. M. 



Mounting Diatoms, &c. — In Mr. Hardy's trans- 

 lation of Professor Brun's "Natural History of 

 Diatoms " are certain directions for the preparation 

 of diatoms for microscopic examination of those 

 organisms ; I am about to give what is probably a 

 needless piece of advice, viz. don't try them, as 

 most of the processes are old and worthless. The 

 plan of burning on the cover has long been known, 

 and if carefully conducted is of use, as it shows the 

 natural position of the valves in the filamentous and 

 stipitate conditions of the Diatomaceae ; but if the 

 preparer possesses the "magic of patience" a much 

 better preparation may be made by macerating the 

 diatoms in strong methylated alcohol, which extracts 

 the endochrome ; the stained alcohol should be 

 poured off from time to time and replaced by fresh 

 (the last addition should be pure spirit) ; the diatoms 

 should then be washed with pure distilled water, 

 and when mounted should be dried on the cover or 

 slide and not burnt. Professor Brun's directions for 

 cleaning diatoms possess no advantage over the usual 

 plan ol boiling in nitric acid, &c., the modus operandi 

 of which have frequently been described in this 

 journal. The preparation of balsam objects would 

 result in a failure if the directions given by Professor 

 Brun are followed : in the course of a few hours 

 or days the frustules would have an " air bubble " or 

 vacuole, and even detached valves would be in the 

 same predicament. In confirmation of this, let a 

 drop of, S3.y Melosira varians in filament, be dried on the 

 slide or cover and essence of turpentine (terebinthine) 

 be dropped upon it until the frustules are filled, and a 

 smaller -quantity of Canada balsam in a viscid state 

 be placed upon it ; if this is at once hardened the 

 turpentine is drawn out of the frustules and a so- 

 called air-bubble is the result. The turpentine 

 simply fills the frustule, and if the balsam is boiled 

 the turpentine is vaporised and is driven out and 

 combines with the hardened balsam, which becomes 

 too viscid to take its place within the frustule. I 

 am not aware that a prism could be used for the 

 purpose of picking out, or that magnification could 

 be obtained by means of a prism ; another, and I 

 think insuperable, difficulty in the use of glycerine is 



the impossibility of detecting delicate forms when 

 immersed in that medium, its refractive index being 

 nearly the same as that of the diatom valve. Pro- 

 fessor Brun, in liis remarks on the reproduction of 

 diatoms, says "that numerous observations have 

 proved that their reproduction takes place, first, by 

 germs (sporules) ; second, by direct deduplication ; 

 and third, by reproductive sacs (spores) which result 

 from the deduplication." It is by no means proved 

 that reproduction ever takes place by means of germs 

 (sporules), and in the succeeding paragraph he states 

 that "the spores are so minute that they have 

 hitherto escaped the eye of observers aided by the 

 best immersion lenses." Their existence is therefore 

 at best but hypothetical, and not a proven fact. His 

 third method is not easy to comprehend, but I 

 suppose it to mean the production of a sporangial 

 frustule, but the result of this is not the production 

 of sporules, but of a frustule many times larger than 

 the parents. My remarks of course apply to Mr. 

 Hardy's translation, as I have not seen the original 

 paper, but I have no doubt as to its substantial cor- 

 rectness. I notice that the sign ■\- is used instead 

 of X , the usual sign for magnification, and " slender " 

 instead of "thin" covers, but the meaning is easily 

 understood. — F. Kit ton, Hon. F.R.M.S, 



Tubes for conveying Moist Specimens, 

 DiATOMACEA, MuD, &c., BY PosT. — A thin mem- 

 brane of gutta percha, such as used by surgeons, 

 cut to the required size ; the joint made by dipping 

 a camel-hair brush in chloroform, drawing it along 

 the edge, say half an inch wide, then placing the 

 part to be joined to it before the chloroform has 

 evaporated ; the operation is simple. Do not fill 

 your tubes quite full, say three parts ; this will allow 

 of a little pressure, should it occur in transit. The 

 cover made by rolling brown paper over a ruler or 

 other suitable form, fastening with paste, as fire-work 

 cases are made, allowing to dry, then cut to lengths 

 required ; attach label with address and stamps. — 

 7. J. M., Tredegar. 



ZOOLOGY. 



Pugnacity of the Caterpillars of Antho- 

 CHARis Cardamines. — Although I have had various 

 species of larvje of butterflies and moths crowded 

 together in boxes, and although in one instance at 

 least I was not without suspicions of cannibalism 

 when the natural food ran short, I have not noticed 

 any actual combativeness except in the case of the 

 caterpillars of A. Cardamines. On one occasion I 

 saw two of these in conflict. One was attached by 

 the posterior half to the upper extremity of a twig, 

 the tail being uppermost and the anterior portion of 

 the body dependent and arched, serpent-like, in 

 antagonism to the similarly arched head and neck 



