Genes are distinct regions of a chromosome.

Endocrine glands are ductless and discharge their secretions into the blood or tissue fluid.

When an electrical impulse is stimulated in a nerve, the impulse travels down its axon to the end of the nerve, which is called a __________.

The fibrous outer covering of bone is called the __________.

Deciduous teeth are:

Fertilization of the egg must occur within 48 hours.

Sperm are produced in the __________.

When an electrical impulse is stimulated in a nerve, the impulse travels down its axon to the end of the nerve, which is called a __________.

The section of bone that articulates with other bones is called the __________.

The stomach has _____ layer(s) of muscle.