First heart sound is produced during closure of auriculo- ventricular or AV node. The first sound is lubb. It is low pitched and is of long duration. It is produced by tight closure of bicupsid and tricupsid valve at the start of ventricular contraction.

Motor neurons are efferent neurons and are located in CNS. The impulse acts in two direction. It carry impulses from the brain and spinal cord to muscles or glands. hen a stimulus is received by a sensory neuron, the impulse (or message) is carried through fibrous extensions called dendrites to the cell body.

Nucleated RBCs are found in Camel and  Leama, which is an exception in biology.

In the process of excretion, DCT or Distal Convoluted Tubule extracts the wastes like uric acid during the formation of urine. It takes place during tubular secretion or augmentation.

Haemoglobin in earthworm is dissolved in plasma. It is a protein in RBCs to carry oxygen around their bodies. It is not found in the corpuscles like the vertebrates but is found dissolved in plasma.

The pH of protoplasm is 6.8.

Acrosome secrets a lytic enzyme hyaluronidase, which help in the penetration of ovum.

Earthworms are hermaphroditic i.e., functional reproductive organs of both sexes occur in the same individual. The eggs of one individual, however, are fertilized by the sperm of another individual, i.e. cross fertilization. During mating two earthworms are bound together by a sticky mucus while each transfers sperm to the other.

Adrenal gland secretes adrenaline hormone which is sympathomimetic and it works opposite to pressure. 

Muscular movements of alimentary canal are known as peristalsis. These movements occur in the oesophagus, stomach and intestines.

Diastole is the phase of the heartbeat when the heart muscle relaxes and allows the chambers to fill with blood.

Systole is the last stage of a heart beat.

A muscle contraction is isotonic if muscle tension remains the same throughout the contraction.