restriction. n. 1. something that restricts; a restrictive measure, law, etc. 2. the act of restricting or the state of being restricted. 3. (Logic) logic maths a condition that imposes a constraint on the possible values of a variable or on the domain of arguments of a function.
The primitive gut that forms during gastrulation in the developing embryo is known as the archenteron or the digestive tube.It develops into the digestive tract of an animal.ach is controlled by the dorsal blastopore, and primitive node (also known as Hensen's node), respectively. During Gastrulation, the Archenteron develops into the digestive tube, with the blastopore developing into either the mouth (Protostome) or the anus (Deuterostome).
Structure. The primitive brain of the earthworm consists of two cerebral ganglia. Sensory nerves leave the brain and run forward to the first segment in the earthworm's body. The nerve cord travels from this first segment to the last.A fibrous sheath surrounds the nerve cord.hile humans and other vertebrates have a spinal column that runs down their back, or dorsal side, earthworms possess a nerve cord consisting of two strands that runs down their belly, or ventral side.