In article <50hd6j$4op at decius.ultra.net> wiemanh at ma.ultranet.com (Henry M. Wieman) writes:
>From: wiemanh at ma.ultranet.com (Henry M. Wieman)
>Subject: left-right reversal of CNS: Why?
>Date: Tue, 03 Sep 96 12:41:55 GMT
>Why does the CNS have right and left reversed in relation to rest of the body?
Cajal put forward a very plausible explanation based on the
fact that images on the retina are left/right inverted.
Without the visual and motor decussations it would need peculiar
and complicated circuitry to make a movement of one side of the
body that related to something in the ipsilateral visual field.
See his "Recollections of my Life" for a concise explanation
with diagrams.
>Specifically, do any invertebrates show the reversal?
Yes. This is cited in support of the withdrawal-from-harmful-contacy
theory. See Sarnat & Netsky: Evolution of the Nervous system.
John A. Kiernan
Department of Anatomy
Univ. of Western Ontario
LONDON, Canada N6A 5C1
e-mail: kiernan at uwo.ca
