200 



SCIENCE-GOSSIP. 



[Sept. ], 1865. 



live for hours without its head. No doubt many a 

 young reader, and perhaps some old ones too, will 

 wonder at this fact, and look for an explanation. 



The fact becomes interpreted when it is known 

 that flies, in common with other insects, do not 

 breathe through their mouths and heads, but have 

 a special and peculiar organization for carrying on 

 this important and natural operation of life. 



The head of the fly contains the compound eyes 

 with which it sees; the mouth and tongue, with 

 which it feeds, but cannot make sounds ; and the 

 antenna;, which are variously set down as organs of 

 hearing, smelling, and feeling ; whilst some say that 

 they may be organs of a sense of which we may 

 have no idea. 



The body it is which contains the breathing 

 apertures ; these form a series of pores along each 

 margin of the under surface, and are called spiracles, 

 or stigmata. 



The spiracles of insects form beautiful micro- 

 scopic objects, and the amateur frequently makes 

 the attainment of a number of them from different 

 insects, one of his first designs in his earliest efforts 

 at the preparation and mounting of objects. This, 

 no doubt, arises from the great beauty of the pre- 

 parations, and the ease with which subjects are 

 obtained for dissection. 



One of the best microscopic handbooks says that 

 the " spiracles are generally visible on the exterior 

 of the body of the insect, especially on the ab- 

 dominal segments," and that "they are easily dis- 

 sected by means of a knife or a pair of scissors." 



This statement, generally correct, and suflicient 

 in the case of the Water-beetle {Di/tlscus), the Cock- 

 chafer, and other insects, fails in the case of the 

 Blow-fly ; and the amateur will have much trouble 

 and frequent disappointments in his endeavoiirs, 

 under this guidance, to discover the spiracle of the 

 fly, so beautifully figured in the same handbook. 



I make these observations, not to find fault witli 

 my handbook, which I value as one of my best 

 books, but to show the necessity and utility of such 

 practical hints as can be best given througli the 

 medium of such a publication as Science Gossip. 



The spiracles usually mounted are situated in the 

 thorax, near to the head. 



There are four spiracles in the thorax, two near 

 the head, and two near the wings ; they are not 

 easily seen, and may be mistaken and not found. 



To obtain them, first steep the fly in liquor potassae 

 for a week, then remove the head and abdomen, and 

 divide the thorax into two parts, cutting it down 

 along the centre of the back. The muscles, &c., 

 can now be easily removed, leaving the two portions 

 of skin tolerably clean ; these must be well washed 

 in water, on a glass slide, with a camel-hair pencil, 

 until every remaining portion of muscle and trachea 

 be completely removed. Tlie spiracles will now 

 appear under the microscope, or even to the naked 



eye, if they be held up against the light, as small 

 oval openings ia the skin. 



The cleaned skin should now be placed on a glass 

 slide and covered with a piece of strong glass, and 

 subjected to gentle and constant pressure until it 

 becomes nearly quite dry. It should then be steeped 

 in clean turpentine for a few days (prolonged steep- 

 ing bleaches too much), when it may be taken out, 

 trimmed round the edges, and mounted in balsam. 



Fig. 1. Spiracle near the head. 



The spiracle near the wing I have never seen 

 figured in the handbooks, or mounted by the pro- 

 fessional artist, yet it is interesting from its pecu- 

 liarity. In it the branching proceeds from one side 

 only ; and its position in the body of the insect is 

 not symmetrical, being placed perpendicular rather 

 than parallel to the direction of the spiracle near 

 the head. There are spiracles in the abdomen also, 

 but they are very small, and not worth mounting. 



Fig. 2. Spiracle la'di the wing. 



I would fain give some directions to the inexpe- 

 rienced amateur ia microscopy as to the spiracle of 

 the larva of the fly, but I find I have done enough 

 for one occasion. The subject, though humble, wijl 



