Hemichordate Nerves

Cross references:    Hemichordates      Hemichordate Hormones     
Hemichordate Neurotransmitters      Hemichordate Genomics

Hemichordata (Wiki) 
http://en.wikipedia.org/wiki/Hemichordata 
"They seem to have a primitive form of notochord, formed from a diverticulum of the foregut called a stomochord, but this is most likely the result of convergent evolution rather than homology with the vertebrate notochord. A hollow neural tube exists among some species (at least in early life), probably a primitive trait they share with the common ancestor of chordata and the rest of the deuterostomes.

The biology of Hemichordata and Protochordata (Open Library)   

    This is an online card catalog.  It doesn't provide online documents, but it tells you where to find hard copies of books.  Using it, I found a hard copy of:   

The biology of Hemichordata and Protochordata
. by E. J. W. Barrington
Published in 1965, Oliver & Boyd (Edinburgh, London).
The biology of Hemichordata and ...
openlibrary.org/b/OL13582217M -

    The diagram, below, is from this hardcopy.  I photocopied the page in the book and then scanned the photocopy. 
 

Page 33




My comment:   
    What interests me most about the diagram is the way the axons from the nerves in the 'collar nerve cord' cross before entering the 'circular connective' and the 'dorsal nerve cord of trunk'.  This is called a "decussation", and is found in all of the acorn worm's descendants, including we humans. 

Decussation (BTB) 
http://thebrain.mcgill.ca/flash/i/i_06/i_06_cl/i_06_cl_mou/i_06_cl_mou.html
    " Next, at the junction between the medulla and the spinal cord, the fibres of this lateral corticospinal tract cross the midline and continue their descent on the opposite side of the spinal cord. About 80 to 90% of the axons from the motor cortex undergo this crossover, or decussation, before reaching the motor neurons responsible for the movement of the most distal segments of the arms and legs.
My comment
    Click the link to see the picture.   





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