Insect skeleton 



WHOLEMOUNTS IN RESINOUS MEDIA 



63 



acetic acid and then transferring it from 

 this acid to balsam. Many small insects, 

 or other arthropods, are too opaque for 

 this method of preparation to render ap- 

 parent any details of the endoskeleton, 

 which is so frequently necessary for diag- 

 nostic purposes. These forms must, there- 

 fore, be skeletonized and rendered par- 

 tially transparent before mounting. 



Insects are skeletonized witli 10% po- 

 tassium hydroxide, which dissolves and 

 removes the internal organs while at the 

 same time softening the skeleton suffi- 

 ciently for the specimen to be flattened 

 and made into a wholemount. Some very 

 skilled mounters of the past made a spe- 

 cialty of preparing whole insects without 

 pressure, but these specimens are chiefly 

 valuable as exhibits, and not as sUdes for 

 study. 



Let us suppose that we have an ant 

 which is to be made into a transparent 

 wholemount. It does not matter whether 

 this specimen has been freshly collected 

 or has been dried for some time; in either 

 case it must be soaked for at least three or 

 four days in 95 % alcohol. Unless this pre- 

 caution is taken, the strong alkali will dis- 

 solve the thin membrane which holds the 

 joints together and the specimen will fall 

 to pieces. Disregard of this simple precau- 

 tion is responsible for more failures in this 

 type of mount than anything else. After 

 the specimen has been satisfactorily hard- 

 ened in alcohol, it is transferred to water 

 until it is rehydrated and then placed in 

 the alkali. In the case of old and hardened 

 specimens it is desirable first to drill a fine 

 hole at the tip of the abdomen with a 

 sharp needle. After 24 hours in the alkali, 

 the specimen should be removed and 

 stranded on a glass shde with the legs 

 more or less in the position in which they 

 will be mounted. The s{)ecimen is then 

 gently stroked with a brush from the point 

 of the head toward the tip of the abdomen, 

 care being taken not to break off any of 

 the appendages. The purpose of this 

 stroking is to expel any of the viscera 

 which may have been dissolved, either 

 through the natural vent, or the small one 

 which has been made with a needle. It has 

 been stated that the specimen which we 

 are examining, an ant, may be left for 24 



hours before this is done, but in the case of 

 thinner-walled and more delicate speci- 

 mens, stroking must be done two or three 

 times a day. The reason for this is that 

 the hydrolysis of the internal organs 

 causes great swelling and, unless some of 

 this fluid is expelled at frequent intervals, 

 the abdomen, thorax, and even the head 

 will be swollen and stretched into an un- 

 natural appearance. The process of gently 

 stroking out the contained material either 

 once or twice a day is continued until it is 

 apparent that no further viscera remain 

 in the animal. It must be emphasized 

 again that it is quite impossible to make a 

 good preparation if the specimen is just 

 thrown into alkali and left there until it is 

 sufficiently transparent. When all the vis- 

 cera have been removed, the appendages 

 are carefully arranged with needles as the 

 specimen lies stranded on the slide, and a 

 few drops of glacial acid dropped onto the 

 specimen from a pipet. This instantly ren- 

 ders the specimen transparent and at the 

 same time partially hardens the append- 

 ages in place. The specimen, however, has 

 yet to be flattened and properly hardened 

 before it can be mounted. A couple of 

 thick covershps, or a couple of pieces of 

 cardboard of the same thickness as that 

 desired in the final specimen, are laid one 

 on each side of the specimen to support a 

 second shde which is then placed on top. 

 It is essential that the specimen should be 

 flattened without producing any wrinkles 

 in the softened chitinous exoskeleton and, 

 unless the insect is naturally flat, this can- 

 not be done merely by dropping a shde on 

 top of it. Instead, the brush which was 

 previously used for stroking is turned side- 

 ways, and rolled backward and forward 

 along the insect, pressing out any wrinkles 

 which may appear. A second slide is 

 placed on top to hold the insect flat and, 

 with the appendages in the position de- 

 sired, two shdes are tied or chpped to- 

 gether and placed in a jar of 95% alcohol 

 until they are next required. They should 

 not remain in alcohol for less than a week 

 and may remain for an indefinite period 

 without damage. After the specimen has 

 been hardened and dehydrated in this 

 manner, the two sUdes are very carefully 

 separated, with the use of a fine pipet to 



