Malpighian tubules :

There are 72 to 90 malpighian tubules which are attached in 6 groups of 12 to 15 at the junction between the midgut & hind gut. The malpighian tubules are long & narrow tubules which are yellow and unbranched. They rennan freely suspended in the heaemolymph. The length of the tubules is about 26 mm & the the diameter is 0.5 mm. The wall of the malpighian tubules is thick & is made up to 6 large cuboidal cells. The lumen is narrow & has ciliated or brush border lining. It is surround by a peritoneum.

Physiology :

Each malpighian tubule is divisible into 2 parts-

1. Proximal half absorptive part.
2. Distal half secretory part

The distal half part of the malpighian tubule take CO₂. H₂O, sodium urates & potassium urates from the haemolymph and secrete them into its lumen. In the lumen CO₂, H₂O. react to form H₂CO₃ which dissociate to form H⁺ & HCO₃^– Similarly, the sodium & potassium utrates ionized to form Na⁺, K⁺ & urate ions. These ions react together & finally form uric acid, sodium bicarbonate & potassium bicarbonate.