Meristic variations involve any change in the number of body parts. In other words, it may be defined as the numerical variation in the taxonomic characters, e.g., number of spots, vertebrae, etc.

Allantois is an extraembryonic membrane developed as an outgrowth from hindgut. In the eggs of reptiles and birds, it functions as a urinary bladder and stores the waste excretory products. It also provides oxygen (in reptiles, birds and mammals) and food (in mammals) to the embryo.

The term 'pelvis' is common to both kidney and skeleton in mammals. In relation to the kidney, it can be described as a chamber in the kidney into which the urine drains from renal tubules before passing to the ureter. For skeleton, it is related with a pelvic girdle or hip girdle.

The formation of urea from NH₃, and CO₂ Occurs in the liver. Through Ornithine cycle or Krebs Hansleit cycle. All the steps of this cycle are enzymatic and can be visualized as follows.

Blood is a living, vascular, fluid connective tissue, which is made of 60% plasma, 40% of blood cells and platelets.

Class-Ostracodermi of vertebrata includes most primitive vertebrates, e.g., Cephalaspis and Drepanaspis.

Neutrophils are most abundant granulecytes which engulf microbes by phagocytosis. These have 2-7 lobulated nucleus and do not stain any basic or acidic dye monocytes are large sized leucocytes, which are highly motile and phagocytic in nature.

The deficiency (hypovitaminosis) of vitamin-B₁₂ or cyanocobalamine causes pernicious anaemia, demyelination of nerve fibres and glossitis (inflammation of tongue).

Theory of continuity of germplasm was proposed by August Weismann (1892), a German Biologist, he suggested that the changes occurring in germplasm are inherited by offsprings, whereas in somatoplasm are not transmitted to next generation.