{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

BSsqans-lect20 chordata

BSsqans-lect20 chordata - BIS 1B(Winter 2008 Study question...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
BIS 1B (Winter 2008) Study question answers: Chordata Lecture 20 1. One of the traits that Chordates and Hemichordates share is pharyngeal gill slits. Can you trace the phylogenetic history of these gill slits through the various classes of chordates to mammals like yourselves? Briefly, pharyngeal slits begin as feeding structures in the tunicate larvae and lancelets permitting water to enter the mouth exit the pharynx without interruption. In the fishes these slits first take on a respiratory function, acquiring gills on each reinforced arch, then combining with muscles to form a respiratory pump. Later particular arches variously become other structures including jaws (the anterior set). In amphibians more of these arches loose their respiratory function and become parts of the skull and throat bones. In the amniotes all respiratory function is lost as these bones variously become associated with the skull, hearing and vocal mechanisms. 2. Our nervous system is internal, yet it is derived from ectoderm. Explain how the internal nervous system can be formed from the outer ectoderm during the course of development. A plate (Neural plate) of ectodermal tissue differentiates from the rest of the ectoderm along the dorsal midline of the developing embryo. This ribbon of tissue begins to curl up at the edges gradually
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}