The excretory organs are a pair of kidneys. They are dark red, three lobed structures. They open separately into the urodaeum of the cloaca through two different ureters. There is no urinary bladder.The urine is excreted in the form of uric acid, a semi solid white mass discharged along with faeces through the cloacal aperture.
The male has a pair of oval testes. From each testis, a duct, the vasdeferens, passes back and opens into the cloaca. The vas deferens is dilated at its posterior end into a seminal vesicle. There is no copulatory organ.
Only the left ovary persists in the adult. The right ovary disappears during development. The ovary and the oviduct of only oneside are functional during breeding season.
Sub phylum - Vertebrata
Class - Aves
Order - Columbiformes
Type - Columba livia
Birds are easily recongnised group of vertebrates. In birds every part of the body is modified to suit their aerial mode of life. Birds possess feathers, beak and feet modified in relation to their aerial life.
The Pigeons are flying birds(carinate). They are known both as wild and domesticated forms. The Pigeons are seen both in tropical and temperate zones. About 10 species of Pigeons are found in India. The pigeons fly in flocks and roost together. The domestic pigeons have many varieties, namely panter, fantail and tumblers. They differ in size, colouration and feather ar-rangement. All of them are, however, descendants of the rock pigeon-columba livia.