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).
Lampreys and hagfishes are the only jawless vertebrates to survive today. They both have a round mouth and for this reason are often referred to as cyclostomes. They are the most primitive of the vertebrates. By primitive, a biologist means that they are the least changed from the first vertebrates.1  They have no paired pectoral (shoulder) or pelvic (hip) fins. 2  Their notochord persists for life, never being completely replaced by a backbone even in the lampreys.3  They have no scales.y primitive, a biologist means that they are the least changed from the first vertebrates. 1  They have no paired pectoral (shoulder) or pelvic (hip) fins. 2  Their notochord persists for life, never being completely replaced by a backbone even in the lampreys. 3  They have no scales.