Insect Abdomen: Appendages found on the abdomen

Insect abdomen is the third functional region of insect body. It is located behind the thorax and contains 6-10 segments. There are various types of appendages arise from the abdomen.

Cerci

Located close to anus.

-Blattodea: simple and jointed cerci

Via ediacaran.mech.northwestern.edu

-Orthoptera: simple and not jointed cerci

-Dermaptera: Sclerotized, forceps like cerci

Dermaptera forcep like cerci via gallurapestcontrol.com

-Thysanura: Long filamentous cerci

Long filamentous cerci of Thysanura

-Ephemeroptera larvae: Wing like cerci that helps to move forward in water.

Wing like cerci -Ephemeroptera larva

Styles

Can be seen in Cockroach and Lepisma. It is regarded as the vestige of the walking limb.

via microscopy-uk.org.uk

Median caudal filament

This is a thread like projection arising from he center of the last abdominal segment between the cerci.

Abdominal Prolegs

Can be seen in Lepidopera.

via entomology.umn.edu

Abdominal Gills

These are respiratory organs and found in nymphs of some aquatic insects.

Cornicles

These are located dorsally on the abdomen as paired secretory structures.

      

Female External Genitalia

Ovipositors are used for oviposition and it is formed by the modification of 8-9 abdominal segments. Thysanura, Orthoptera, Thysanoptera and some Hymenoptera insects contain true ovipositors.

Ovipositor places egg inside caterpillar 

Egg is released (naturecloseups.com)

-The ovipositor is modified as a poison injecting sting ( Wasps, bees..etc)

via amazingnature.us

-Hind end of the abdomen is extended to work as an ovipositor

Male genitalia

Modification of 9^th abdominal segment makes the copulatory organ of males which is consist of aedeagus and pair of lateral claspers to grasp and hold the abdomen of the female during mating. 

Special reactions/tests for Urea, Formamide, Oxamide, Salicylamide, Succinimide, Phthalimide

Urea

Urea nitrate and oxalate: Take a concentrated solution of urea, to one portion, add a few drops of con. HNO₃: the white crystalline urea nitrate (m.p. is 163°) is precipitated; to another portion, add con. Oxalic acid solution and scratch with a glass rod. White crystals of urea oxalate (m.p. is 171°) are separated. In an excess of water both salts dissolve.

Biurate reaction: Take 0-2 g of urea into a dry test-tube and heat gently above the melting point. NH₃ is evolved. After 2 minutes the liquid rapidly solidifies with the formation of biuret.

2NH₂CONH₂à NH₂CONHCONH₂ + NH₃

Dissolve the solid residue in a few ml. of warm 10% NaOH solution. Stand it to cool and add 1 drop of dil. CuSO₄ solution. A purple coloration is obtained. A pink/purple coloration is due to containing two -CONH- groups attached to one another, or to the same carbon atom or nitrogen atom. Therefore the same colouration is also given by malonamide, oxamide and by proteins/peptides.

Urease test: Urease enzymes can hydrolys Urea to Ammonium carbonate. The reaction is specific. It is used for solutions of urea to which the biuret test cannot be applied.

Action of hypobromite: Add sodium hypobromite solution to a solution of urea. The brisk effervescence is given.

NH₂CONH₂ + 3NaOBr à N₂ + CO2 + 3NaBr + 2H₂O

Formamide

Boil 1 ml of formamide in a test-tube. NH₃is evolved from it.  CO is produced, but cannot be ignited in the presence of the NH₃.

Oxamide

Biuret test: Oxamide does not need any preliminary treatment to proceed with the test. Shake 1 g of oxamide with 1ml of 10% NaOH solution. Add 1 drop of very dilute CuSO₄ solution to it and mix well. A pink coloration is produced.

Sulphuric acid test: Heat 0-3 g of Oxamide with con. H₂SO₄. CO and CO₂ are evolved.

Salicylamide

FeCl₃ coloration: Take the solid into a test tube. Add FeCl₃ solution and shake. An intense violet coloration is produced as the Phenolic groups are present.

Succinimide

Reduction: Take about 1 g of succinimide and an equal amount of Zn dust into a dry hard-glass test tube and mix well. Heat strongly. Soak a pinewood splinter in con.HCl and place it in the mouth of the tube. The splinter is turned red by the vapour of pyrrole which is formed by reduction.

Fluorescein reaction: Take about 1 g of Succinimide, 1 g of resorcinol and 2 drops of con. H₂SO₄ into a dry test tube and fuse all of it together. Cool and add water. Then add NaOH solution in excess. A green fluorescent solution is produced.

Phthalimide

Phthalein reaction: Take about 1 g of Phthalimide, 1 g of phenol and 2 drops of con. H₂SO₄ into a dry test-tube and fuse all together very gently. Let it cool and add water. Then add NaOH solution in excess. A red coloration is produced which is decolorized by acids.

Fluorescein reaction: Repeat the above test, using resorcinol instead of phenol. A green fluorescent solution is produced on the addition of NaOH solution.

Physical properties of common organic compounds (In brief)

One of the easiest ways to get an idea about an unknown organic substance is to check for its physical properties first. Physical properties are appearance, state, odour, colour, solubility in water etc. Below are some general physical properties of common organic substances.

Odour

Fruity odour: Esters, ethers.

Odour of almonds: Benzaldehyde, Nitrobenzene, Benzonitrile,

Pungent odour: Pyridine, Formic acid, Acetic acid, Benzoyl chloride, Benzyl chloride, Acetyl chloride.

Many phenols give a unique Phenolic odour. Also some derivatives of salicylic acid such as Salicylaldehyde.

Colour

Orange: Ortho-Nitro-aniline, Alizarin.

Yellow:  Quinones, m-nitroaniline, o-nitrophenol, and many other nitro-compounds. Also Iodoform.

Red: i,2-Naphthoquinone.

Blue: Commonly Copper salts.

Solubility in water

Soluble in cold water: Lower aliphatic alcohols, lower aliphatic aldehydes & ketones, lower aliphatic nitriles, lower aliphatic acid chlorides, aliphatic amines, pyridine, salts of amines, glycine, some phenols, aliphatic acids, sulphonic acids, ammonium salts and alkali salts of all acids, methyl esters of certain acids such as  formic, oxalic, succinic and tartaric. Also some aliphatic amides and imides, such as succinimide.

Almost insoluble in cold water: Higher ketones, most esters, ethers, higher alcohols, higher phenols, Benzyl alcohol, metaformaldehyde, Aromatic aldehydes, aromatic acids, aromatic amides, aromatic imides, aromatic amines, aromatic nitriles, aromatic acid anhydrides, aromatic acid chlorides, sulphonamides, sulphonyl chlorides, starch, anilides, uric acid, hydrocarbons.

Hydrolysed with water: Acids, esters can hydrolyse easily. Acid anhydrides, acid chlorides, salts of amines and nitrophenols.

Using  litmus-paper on a solution

Weakly acidic: Phenols. Except for nitrated phenols, phenols do not liberate CO₂ from Na₂CO₃ solution.

Weakly alkaline: Alkali salts of some weak acids and pyridine.