1891.] MICROSCOPICAL JOIJENAL. 105 



amination at home. In addition to these advantages for study, out-door 

 excursions for the collection of objects of natural history, botanical 

 specimens, and infusoria take place ever}- other .Saturday afternoon 

 during the summer months, and are generally accompanied by some of 

 the veterans in the art of collecting and instructing. The club pub- 

 lishes an illustrated journal every quarter, containing the papers read, 

 and their discussion. The subscription to this club is ten shillings per 

 annum, and without entrance fee. 



Other Objects. — The blow-fly's tongue has always been a favorite 

 object whether fulfilling its mission as a test object for flatness of field 

 of view, or simplv on account of the beauty of its pseudo-tracheae. The 

 blow-flv aflbrds pleasure in many ways ; as furnishing dissections it is 

 unsurpassed. Whether alive or dead it always affords interest, especi- 

 ally in its recentlv-hatched condition. Blow-flies come from what are 

 known in the fishing world as " gentles," which, after enjoying a short 

 existence in this state, enshroud themselves in a brown case, and await 

 that season when, bursting their bonds, they issue as blow-flys. At this 

 period of their lives they are neat and clean. Their internal viscera 

 are free from all contamination of food, and readily take any stain ap- 

 plied. To obtain it in this state of cleanliness, the following plan must 

 be adopted : A hole should be made in a tin biscuit box, and a piece 

 of glass tubing about half an inch in internal diameter passed from this 

 hole through a bung into a clean, dry, wide-mouthed bottle. The 

 chrvsalids of flies, together with the sand in which they are supplied, 

 being put into the tin box. they hatch in time, and as they hatch, find 

 their way into the glass bottle through the tube. Feed such a newly- 

 hatched fly on syrup stained with cochineal, and on dissection the whole 

 alimentary tract can be readily discerned by the color. It is at this age 

 that it will be found easier to lay out the proboscis in the usually ac- 

 cepted stvle. while the wings under an air-pump will often expand into 

 bladders, as imprisoned air separates the two surfaces when the pressure 

 of the atmosphere is removed. While speaking of the air-pump it may 

 be mentioned that insects may have their tracheal system, injected with 

 carmine stain if they are placed in it under the receiver, and the air al- 

 ternately exhausted and let in, two or three times in succession. The 

 air being drawn out of the tubes during the first process, the carmine 

 runs in to supplv its place during the second. If the insects are color- 

 less and transparent, the color may be traced even up to the tips of the 

 antennae. 



The Demodex foUictilorzim is a minute acarus. which derives con- 

 siderable interest not onlv from its place of habitation, from which it can 

 be easily procured, but also from the lively movements it exhibits when 

 first captured. It varies in lengtli from one-fiftieth of an inch to one- 

 hundredth. If the black spots which often adorn the face of adolescence 

 be squeezed, a little speck of fatty matter exudes ; take this up with an 

 oiled pin, and transfer it to a slide, on which has been placed a little 

 castor-oil, and cover with a thin and therefore light glass cover. On 

 slightly warming this, the fatt\- matter dissolves and clears up, showing 

 the demodex in great activit}-. If the epithelial scales, which help to 

 make up the bulk of the fatty matter, are not so abundant as to hide the 

 acarid. the cover-glass may be cemented down, as the mite is too minute 

 to be ti'ansferred to another slide. 



