Earthworm body plan. Each segment contains a coelomic chamber full of organs. A gut, ventral nerve cord, and dorsal and ventral blood vessels run through all coelomic chambers.

Each of the imaginal disks shown in the larva develops into a specific segment of the adult.

Astrocytes (orange) and a neuron (yellow) in brain tissue. The cells in this fluorescence micrograph were made visible by use of a light-emitting tracer.

Birth relies on neural signals from the uterus and on maternal hormones that act on the uterus In response to sensory neural input arising from the push of the fetus ...