BIO354H5 Lecture Notes - Lecture 2: Gastrulation, Hemichordate, Notochord
Document Summary
Mouth and anus - 2 ends of the embryos. There is a notal chord - stiff rod - advanced by spinal column. This whole form of chordate exist in water - no life on land at this time. Fish - live in extreme conditions and always in water. Fish are one of most abundant species in the world. Chordates - notochord and dorsal hollow nerve cord. Both have digestive tract and solid nerve cord. If neural cord is not hollow - there is an impediment to transition which would make an animal not do anything - animal would not move. If neural cord is hollow - there is no impediment to transition. Thick nerve cord cannot get impulses across - humans have a hollow nerve cord which allows us to generate and send/receive nerve impulses across the spinal cord. Because nerve cords are restricted in size - octopus has found way around it.
