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|Title: ||Some aspects of the anatomy of the alimentary canal of the lesser octopus, Eledone cirrhosa (Lamarck 1817), with special reference to the nervous system|
|Authors: ||Polglase, Jane L.|
|Supervisors: ||Cobb, James L. S.|
|Issue Date: ||1980|
|Abstract: ||The modern cephalopod molluscs, particularly the octopods, are
highly developed macrophageous predators which have a pronounced ability
to learn. Striking resemblances are found between these animals and the
vertebrates, particularly the fish. The study of cephalopods therefore
provides an opportunity to examine systems which are composed of structural
units common to molluscs but which may be similar in function and performance
to those of vertebrates. This investigation concerns the alimentary canal
and its innervation in the lesser octopus Eledone cirrhosa.
Detailed anatomical investigation shows the alimentary canal of E. cirrhosa to be very similar to that of the better known Octopus vulgaris. Current concepts of the functions of the alimentary organs are discussed utilizing data from both E. cirrhosa and O. vulgaris.
Silver staining reveals a basic pattern of innervation in the alimentary organs. Large nerve trunks running in the external collagenous layer give rise to a nerve plexus within the circular muscle. The longitudinal muscle plexus arises from branches of the circular muscle plexus
or direct from the nerves of the external layer, Nerves of both plexuses
contact muscle fibres in an 'en passant' manner. Fibres run out from the
longitudinal muscle to the subepithelium, where they are observed associated
with muscle fibres and beneath the epithelial basal lamina. Good evidence
for fibres crossing into the epithelium was observed only in the cuticularized
regions of the digestive tract. The digestive gland ducts differ
from this pattern in the very large numbers of major nerves seen in their
external and muscular regions. Outwith the alimentary ganglia nerve cells
are only regularly observed within the major intestinal nerves. Receptor
like cells were also repeatedly observed only in the posterior intestine.
These results axe compared with data from O. vulgaris and the
physiological evidence for the presence of receptors. The blood vessels
of the alimentary canal are innervated at all levels. The distribution
of other densely staining cells is reported.
Evidence for the presence of particular neurotransmitters within
the alimentary canal and alimentary nerve centres is reviewed. Fluorescence
histochemistry shows that at least two types of nerves are present in the
alimentary wall. The majority axe aminergic (including those associated
with blood vessels and some sphincters), as the pattern of fluorescent
nerves is predominantly that shown by silver studies. However, fluorescent
nerves decrease and then disappear anteriorly from the crop/oesophageal
sphincter and posteriorly from the mid-intestine. The stomach has
fluorescent nerves, other than those associated with blood vessels.
Fluorescent fibres enter the gut via the sympathetic and possibly the digestive
gland duct nerves. Non-fluorescent fibres enter via the atrio-rectal
nerves and from the gastric ganglion. The fluorescence is ascribed to
catecholamines as no evidence of 5HT was obtained, Specific fluorescence
was also observed in some cells of the subepithelium and the external
region. These results are discussed with reference to available physiological
The anterior intestine was the representative region chosen for fine
structural studies. These show the alimentary muscles to be the same basic
type (cross or pseudo-striated) as that found in cephalopod somatic or
heart muscle. Three types of myomuscular and neuromuscular junctions axe
described. The presence of mineralized concretions (spherites) in the
external layer of the intestine, together with the complex relations of
its epithelial cells and heavy vascularization suggest a secondary function
of mineral and/or water balance for this organ.
These results are discussed.
Finally, a pathological condition affecting the octopuses during
this study is described.|
|Publisher: ||University of St Andrews|
|Appears in Collections:||Biology Theses|
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